Purification and Partial Characterization of an Endoxylanase Inhibitor from Barley

Hordeum vulgare L. xylanase inhibitor (HVXI), an endoxylanase inhibitor with a protein structure, was purified to homogeneity from barley (Hordeum vulgare L.). HVXI is a nonglycosylated monomeric protein, with a molecular weight of ≈40,000 and a pI ≥ 9.3. Although it inhibits different endoxylanases to a varying degree, the activities of an α‐L‐arabinofuranosidase and a β‐d ‐xylosidase were not inhibited. Apparently, HVXI occurs in two molecular forms. These characteristics and the N‐terminal sequences of the composing polypeptides show that HVXI is homologous with Triticum aestivum L. xylanase inhibitor I, an endoxylanase inhibitor from wheat flour.     

Substrate quality affects microbial‐ and enzyme activities in rooted soil

The rhizosphere reflects a sphere of high substrate input by means of rhizodeposits. Active microorganisms and extracellular enzymes are known to be responsible for substrate utilization in soil, especially in rooted soil. We tested for microbial‐ and enzyme activities in arable soil, in order to investigate the effects of continuous input of easily available organics (e.g., root‐exudates) to the microbial community. In a field experiment with maize, rooted and root‐free soil were analyzed and rhizosphere processes were linked to microbial activity indicators such as specific microbial growth rates and kinetics of six hydrolytic extracellular enzymes: β‐glucosidase, β‐cellobiohydrolase, β‐xylosidase, acid phosphatase, leucine‐ and tyrosine‐aminopeptidase. Higher potential activities of leucine‐aminopeptidase (2‐fold) for rooted vs. root‐free soil suggested increased costs of enzyme production, which retarded the specific microbial growth rates. Total microbial biomass determined by the substrate‐induced respiration technique and dsDNA extraction method was 23% and 42% higher in the rooted surface‐layer (0–10 cm) compared to the root‐free soil, respectively. For the rooted soil, potential enzyme activities of β‐glucosidase were reduced by 23% and acid phosphatase by 25%, and increased by 300% for β‐cellobiohydrolase at 10–20 cm depth compared to the surface‐layer. The actively growing microbial biomass increased by the 17‐fold in rooted soil in the 10–20 cm layer compared to the upper 10 cm. Despite the specific microbial growth rates showing no changes in the presence of roots, these rates decreased by 42% at 10–20 cm depth compared to the surface‐layer. This suggests the dominance in abundances of highly active but slower growing microbes with depth, reflecting also their slower turnover. Shifts in microbial growth strategy, upregulation of enzyme production and increased microbial respiration indicate strong root effects in maize planted soil.     

Glycosidases in soils as affected by cropping systems

Glycosidases are a group of soil enzymes that play a major role in degradation of carbohydrates. This study was conducted to assess the impact of crop rotation and N fertilization on the activities of α‐ and β‐glucosidases and α‐ and β‐galactosidases in plots of two long‐term field experiments at the Clarion‐Webster Research Center (CWRC) and Northeast Research Center (NERC) in Iowa. Surface‐soil (0–15 cm) samples were taken in 1996 and 1997 in corn (Zea mays L.), soybean (Glycine max (L.) Merr.), oats (Avena sativa L.), or meadow (alfalfa) (Medicago sativa L.) plots that received 0 or 180 kg N ha^–1, applied as urea before corn, and an annual application of 20 kg P ha^–1 and 56 kg K ha^–1. Activities of the four glycosidases were significantly affected by crop rotations in both years at the two sites but not by nitrogen application. In general, higher activities were observed in plots under meadow or oat and the lowest in continuous corn (CWRC) and soybean (NERC). Four‐year rotation showed the highest activity, followed by 2‐year rotation and monocropping systems. Linear‐regression analyses indicated that, in general, the activities of the glycosidases were significantly correlated with microbial‐biomass C (r > 0.302, p ≤ 0.05) and microbial‐biomass N (r > 0.321, p ≤ 0.05), organic‐C (r > 0.332, p ≤ 0.05) and organic‐N (r > 0.399, p ≤ 0.01) contents of the soils. Results of this work suggest that multicropping stimulated the activities of the glycosidases. The specific activities of the glycosidases in soils of the two sites studied, expressed as g p‐nitrophenol released per kg of organic C, differed among the four enzymes. The lowest values were obtained for β‐galactosidase and α‐glucosidase, followed by α‐galactosidase and β‐glucosidase.     

Glycoside Hydrolase Family 51 α‐l‐Arabinofuranosidases from Clostridium thermocellum and Cellvibrio japonicus Release O–5‐Feruloylated Arabinose

Arabinofuranosidases act synergistically with other enzymes to depolymerize arabinoxylans by cleaving arabinofuranose substituents from the β‐(1→4)‐linked d ‐xylopyranose backbone. Because arabinose feruloylation is a barrier to some, but not all, arabinofuranosidases, we investigated the actions of three α‐l ‐arabinofuranosidases from the glycoside hydrolase (GH) family 51 on feruloylated arabinoxylan‐oligosaccharide standard compounds with and without feruloyl esterase. GH51 α‐l ‐arabinofuranosidases from Clostridium thermocellum and Cellvibrio japonicus both partially released feruloylated arabinose (up to 59% for C. thermocellum). Simultaneous incubation with arabinofuranosidases and feruloyl esterase quantitatively released arabinose from feruloylated standard compounds. Therefore, although feruloylation does not completely obstruct GH51 arabinofuranosidases, synergistic approaches utilizing multiple enzymes remain the most effective tactic for enzymatic breakdown of feruloylated compounds.     

Characterization of β‐ d‐glucosidase extracted from soil fractions

One way to study the state in which stabilized extracellular enzymes persist and are active in the soil is by extraction from the soil, with subsequent fractionation of enzyme–organomineral complexes and characterization of such complexes. In order to investigate the location and characteristics of soil β‐glucosidase, three soil fractions were obtained both from real (undisturbed) soil aggregates and from structural (dispersed in water and physically disrupted) aggregates using two different granulometric procedures. The β‐glucosidase activity of the fraction was then assayed. When the aggregates were dispersed, more than 73% of activity was in the soil microaggregates with diameters of less than 50 μm (SF₅₀). These aggregates were associated with strongly humified organic matter. Solutions of diluted pyrophosphate at neutral pH liberated active β‐glucosidase from all fractions, although the efficacy of extraction varied according to the type of fraction. The SF₅₀ fraction and aggregates of 2000–100 μm obtained by sieving (SF₂₀₀₀) showed the greatest β‐glucosidase activity (34.5 and 36.0%, respectively). Micro‐ and ultrafiltration of SF₅₀ extracts increased the total β‐glucosidase activity, whereas these procedures, applied to the RF₂₀₀₀ fraction, decreased it. Humus–β‐glucosidase complexes in the SF₅₀ fraction, between 0.45 μm and 10⁵ nominal molecular weight limit ( nmwl ) (SF₅₀II) and < 10⁵nmwl (SF₅₀III) showed an optimum pH at 5.4, and in the SF₅₀I fraction (> 0.45 μm) the optimum was 4.0. The stability of β‐glucosidase in the aggregates of the smallest size SF₅₀II and SF₅₀III decreased at acid pHs. The presence of two enzymes (or two forms of the same enzyme) catalysing the same reaction with different values of Michaelis constant and maximum velocity was observed in all but one of the β‐glucosidase complexes extracted and partially purified from the SF₅₀ aggregates.     

Selected enzyme activities as affected by free iron oxides and clay particle size

Abstract

The effect of soil clay size phyllosilicates, particle size, and iron oxides on the activities of α‐ and β‐glucosidases, phosphomonoesterases, and urease were examined. The two clay fractions (0.2–2 and <0.2 μm) of selected soils had similar mineralogy and were illitic, kaolinitic, and smectitic in composition. In general, enzyme activities were reduced in the presence of clay size phyllosilicates. The montmorillonitic samples were the most effective inhibitors. Activities were generally lower in the presence of the finer clay fractions. The effect of iron oxides on enzyme activities varied. Acid phosphatase activity was significantly influenced by phyllosilicate type, iron oxides, and particle size. The inhibitory effect of phyllosilicates on acid phosphatase activity increased when iron oxides were removed from the clay fraction. Removal of iron oxides, on the other hand, enhanced the activity of alkaline phosphatase. Unlike β‐glucosidase, α‐glucosidase was deactivated in the presence of montmorillonitic and illitic samples regardless of clay particle size. The activity of urease was significantly reduced in the presence of iron oxides.     

Precipitation of enzymes and organic matter by aluminum—Impacts on carbon mineralization

The precipitation of dissolved organic matter (DOM) by aluminum (Al) results in a stable soil organic matter (OM) fraction. Extracellular enzymes can also be removed from soil solution by sorption or precipitation, but whether this affects their activity and their importance for carbon (C) mineralization is largely unknown. We studied the activity of eight extracellular enzymes, precipitated by Al together with DOM, in relation to C mineralization of the precipitated OM. Dissolved OM was obtained from the Oi and Oa horizon of two forest soils and precipitated at different Al : C ratios and pH values to achieve a large variation in composition and C mineralization of precipitated OM. All eight enzymes were present in a functional state in precipitated OM. On average 53% of DOM was precipitated, containing on average 17%–41% of the enzyme activity (EA) involved in C degradation (chitinase, cellobiohydrolase, β‐glucosidase, glucuronidase, lacasse, and xylosidase) previously present in soil solution. In contrast, on average only 4%–7% of leucine‐aminopeptidase and acid‐phosphatase activity was found in precipitated OM. The EA found in precipitates significantly increased the percentage of C mineralized of precipitated OM, with a stronger influence of C‐degrading enzymes than enzymes involved in N and P cycling. However, after 8 weeks of incubation the correlations between EA and C mineralization disappeared, despite substantial EA being still present and only 0.5%–7.7% of C mineralized. Thus, degradation of precipitated OM seems to be governed by EA during the first degradation phase, but the long‐term stability of precipitated OM is probably related to its chemical properties.     

Milling Performance of North European Hull‐less Barleys and Characterization of Resultant Millstreams

Four hull‐less barley samples were milled on a Bühler MLU 202 laboratory mill and individual and combined milling fractions were characterized. The best milling performance was obtained when the samples were conditioned to 14.3% moisture. Yields were 37–48% for straight‐run flour, 47–56% for shorts, and 5–8% for bran. The β‐glucan contents of the straight‐run white flours were 1.6–2.1%, of which ≈49% was water‐extractable. The arabinoxylan contents were 1.2–1.5%, of which ≈17% was water‐extractable. Shorts and bran fractions contained more β‐glucan (4.2–5.8% and 3.0–4.7%, respectively) and arabinoxylan (6.1–7.7% and 8.1–11.8%, respectively) than the white flours. For those fractions, β‐glucan extractability was high (58.5 and 52.3%, respectively), whereas arabinoxylan extractability was very low (≈6.5 and 2.0%, respectively). The straight‐run white flours had low α‐amylase, β‐glucanase, and endoxylanase activities. The highest α‐amylase activity was found in the shorts fractions and the highest β‐glucanase and endoxylanase activities were generally found in the bran fractions. Endoxylanase inhibitor activities were low in the white flours and highest in the shorts fractions. High flavanoid, tocopherol, and tocotrienol contents were found in bran and shorts fractions.     

添加木醋液对沙地土壤微生物生物量和酶活性的影响

[目的]探讨沙地添加木醋液后土壤微生物生物量和酶活性的变化,为沙地土壤生物学质量的改良提供理论依据。[方法]采用盆栽植草培养法,以添加自来水为对照,对沙地添加不同稀释倍数(200,150,100,50,20)木醋液后的土壤可溶性有机碳、氮和酚,土壤微生物生物量碳氮以及土壤酶活性进行研究。[结果]向沙土添加木醋液可以显著降低土壤pH值,显著提高土壤易氧化碳、土壤水溶性碳氮、土壤可溶性酚以及无机氮的含量。在添加木醋液稀释高于50倍范围内,随木醋液稀释倍数降低,土壤微生物生物量碳氮增加以及β-糖苷酶、碱性磷酸酶和脱氢酶活性提高。添加稀释20倍的木醋液,导致土壤微生物生物量碳氮以及β-糖苷酶、碱性磷酸酶和脱氢酶活性有所降低。在高于20的稀释倍数范围内,随着施用木醋液稀释倍数的降低,α-糖苷酶、亮氨酸氨基肽酶、酸性磷酸酶和酚氧化酶的活性有显著增加的趋势。[结论]添加不同稀释倍数的木醋液会影响沙地土壤微生物生物量和酶活性。     

Changes in Distribution of Isoflavones and β‐Glucosidase Activity During Soy Bread Proofing and Baking

Bread made partially with soy may represent a viable alternative for increasing soy consumption in populations consuming Western diets. The potential health‐promoting activity of soy isoflavones may depend on their abundance and chemical form. The objective of this study was to characterize the changes in isoflavone distribution and β‐glucosidase activity during the soy breadmaking process. Soy bread ingredients were combined and mixed to form a dough that was subsequently proofed at 48°C for 1–4 hr and baked at 165°C for 50 min to produce breads. The isoflavone composition and β‐glucosidase activity in bread ingredients, doughs, and breads were monitored. Soy ingredients and wheat flour (not bread yeast) were the major contributors of the β‐glucosidase activity in bread. No degradation of isoflavones was observed during breadmaking but the isoflavone distribution was largely altered. Proofing and baking have important but different roles in changing the isoflavone distribution. Proofing converted isoflavone β‐glucosides to aglycones by highly specific β‐glucosidase activity. Thermal treatment during baking significantly decreased the isoflavone malonylglucosides and increased isoflavone β‐glucosides. Enzyme activity during proofing and the balance between formation and deconjugation of isoflavones during baking determine the isoflavone content and composition in the final product.     

Medium‐ and short‐term available organic matter,microbial biomass,and enzyme activities in soils under Pinus sylvestris L. and Robinia pseudoacacia L. in a sandy soil in NE Saxony,Germany

Total, mobile, and easily available C and N fractions, microbial biomass, and enzyme activities in a sandy soil under pine (Pinus sylvestris L.) and black locust (Robinia pseudoacacia L.) stands were investigated in a field study near Riesa, NE Germany. Samples of the organic layers (Oi and Oe‐Oa) and the mineral soil (0–5, 5–10, 10–20, and 10–30 cm) were taken in fall 1999 and analyzed for their contents of organic C and total N, hot‐water‐extractable organic C and N (HWC and HWN), KCl‐extractable organic C and N (C_org(KCl) and N_org(KCl)), NH ‐N and NO ‐N, microbial‐biomass C and N, and activities of β‐glucosidase and L‐asparaginase. With exception of the HWC, all investigated C and N pools showed a clear response to tilling, which was most pronounced in the Oi horizon. Compared to soils under pine, those under black locust had higher contents of medium‐ and short‐term available C (HWC, C_org(KCl)) and N (HWN, N_org(KCl)), mineral N (NH ‐N, NO ‐N), microbial‐biomass C and N, and enzyme activities in the uppermost horizons of the soil. The strong depth gradient found for all studied parameters was most pronounced in soils under black locust. Microbial‐biomass C and N and enzyme activities were closely related to the amounts of readily mineralizable organic C (HWC and C_org(KCl)). However, the presented results implicate a faster C and N turnover in the top‐soil layers under black locust caused by higher N‐input rates by symbiotic N₂ fixation.     

Feruloylated Wheat Bran Arabinoxylans: Isolation and Characterization of Acetylated and O–2‐Monosubstituted Structures

Arabinoxylan structures vary based on the degree and pattern of substitution of the β‐(1→4)‐linked d ‐xylopyranose backbone with α‐l ‐arabinofuranose units, acetyl groups, uronic acids, and feruloylated side chains. Substitution differences affect arabinoxylans’ physicochemical and physiological characteristics. Wheat bran arabinoxylans were hydrolyzed with GH10 and GH11 endo‐1,4‐β‐xylanases, and feruloylated oligosaccharides were isolated and purified (Amberlite XAD‐2 isolation, Sephadex LH‐20 gel permeation chromatography, and preparative reversed‐phase HPLC). The pure, isolated compounds were structurally characterized via liquid chromatography–electrospray ionization–mass spectrometry and one‐dimensional and two‐dimensional NMR analyses. In addition to the well‐known products of endo‐xylanase hydrolysis (xylotriose and xylobiose O–3‐substituted with a 5‐O‐trans‐feruloyl‐α‐arabinofuranosyl unit on the middle and nonreducing xylose residue, respectively), novel structural features, including O–2‐monosubstitution of xylose adjacent to a xylose carrying feruloylated arabinose, were observed. Additionally, a simultaneously acetylated and feruloylated oligosaccharide has been isolated and tentatively characterized. Oligosaccharides esterified with caffeic acid were also isolated, but these were proven to result, at least in part, as artifacts of the enzymatic hydrolysis.     

Increases in phosphatase and β‐glucosidase activities in wheat seedlings in response to phosphorus‐deficient growth

The ability of plants to utilize P efficiently is important for crops growing in P‐deficient soils or on soils with a high P‐fixing capacity. The purpose of this work was to investigate early physiological changes which occur when wheat (Triticum aestivum L.) seedlings were grown under P‐deficient conditions. Wheat plants were grown in a greenhouse and watered with nutrient solution containing or lacking P. During the interval 12 to 18 days after planting, the dry weight of wheat seedlings was similar regardless of P treatment, although the P‐deficient plants had a greater proportion of the total plant weight in the roots. Sixteen days after planting, the roots and leaves of P‐deficient plants had only 20 to 30% the P content of P‐sufficient plants. After 16 days, plants grown under P stress had 41% more p‐nitrophenol phosphatase activity and 70% more β‐glucosidase activity in shoot homogenates than was found in P‐sufficient plants. Changes in both enzyme activities may be involved in the mobilization of plant resources during the early stages of P‐deficient growth.     

Extraction of β‐Glucan from Oat Bran in Laboratory Scale

Effects of various enzymes and extraction conditions on yield and molecular weight of β‐glucans extracted from two batches of commercial oat bran produced in Sweden are reported. Hot‐water extraction with a thermostable α‐amylase resulted in an extraction yield of ≈76% of the β‐glucans, while the high peak molecular weight was maintained (1.6 × 10⁶). A subsequent protein hydrolysis significantly reduced the peak molecular weight of β‐glucans (by pancreatin to 908 × 10³ and by papain to 56 × 10³). These results suggest that the protein hydrolyzing enzymes may not be pure enough for purifying β‐glucans. The isolation scheme consisted of removal of lipids with ethanol extraction, enzymatic digestion of starch with α‐amylase, enzymatic digestion of protein using protease, centrifugation to remove insoluble material, removal of low molecular weight components using dialysis, precipitation of β‐glucans with ethanol, and air‐drying.     

Release of β‐Glucan from Cell Walls of Starchy Endosperm of Barley

β‐Glucan can be solubilized from barley by warm water, with increasing solubilization as the temperature is increased. Substantially less glucan is extracted if the barley is dehusked using sulfuric acid, particularly if the dehusked barley is denatured. This indicates that enzymes capable of solubilizing glucan are present in barley. Various purified enzymes promote the solubilization of glucan from denatured and dehusked barley. Apart from endo‐β‐(1→3)(1→4)‐glucanase, these enzymes include endo‐xylanases, arabinofuranosidase, xyloacetylesterase, and feruloyl esterase. Ferulic acid and, probably, acetyl groups are esterlinked to arabinoxylan, not β‐glucan, in the cell walls of barley starchy endosperm, so the ability of the esterases, xylanases, and arabinofuranosidase to solubilize glucan indicates the pentosan component of the cell wall can restrict the extraction of glucan.     

Soil microbiological properties and its stratification ratios for soil quality assessment under different cover crop management systems in a semiarid vineyard

In vineyards in Spain, tillage and semiarid Mediterranean climatic conditions accelerate organic matter loss from the soil. Cover crops are a conservation management practice that can provoke changes in soil quality which requires evaluation. Stratification ratios of soil properties such as soil organic C and labile C fractions have been proposed for the assessment of soil quality under different soil management systems. Our objective was to study the effect of different cover crop management on various soil parameters and their stratification ratios. We evaluated three different soil managements in a Typic Haploxerept from NE Spain: conventional tillage (CT); 5‐y continuous cover crop of resident vegetation (RV); and 4‐y continuous cover crop of Festuca longifolia Thuill., followed by 1‐y Bromus catharticus L. after resowing (BV). We monitored soil organic C, particulate organic C, water soluble C, potentially mineralizable N, microbial biomass C, β‐glucosidase and urease enzymatic activities, and water stable aggregates at 0–2.5, 2.5–5, 5–15, 15–25, and 25–45 cm soil depths. We calculated soil depth stratification ratios of those soil properties. Resident cover crop increased microbiological properties, labile C fractions, and aggregation with respect to conventional tillage at 0–2.5 and 2.5–5 cm soil depths. However, for Bromus cover crop the same soil properties were lower than for the resident cover crop at 0–2.5 cm depth. Stratification ratios of β‐glucosidase and urease enzymatic activities, and particulate organic C showed a higher sensitivity than other soil properties; therefore, they would be the best indicators for soil quality assessment in semiarid Mediterranean vineyards.     

Post‐fallow tillage and crop effects on soil enzymes and other indicators

Soil changes induced by crop rotations and soil management need to be quantified to clarify their impact on yield and soil quality. The objective of this study was to investigate the effect of continuous oat (Avena sativa L.) and a lupin (Lupinus albus L.)‐oat rotation with and without tillage on soil enzymes, crop biomass and other soil properties In year 1, oat and lupin were grown in undisturbed plots or in plots subjected to disc tillage. Crop residues were incorporated before oat was sown in year 2 in the disc‐tilled plots or remained on the soil surface of untilled plots. Soil samples were collected regularly and analysed for pH, organic C, Kjeldahl‐N, mineral N, extractable P, and the enzyme activities of β‐glucosidase, cellulases, acid phosphatase, proteases, urease, and culturable bacteria and fungi. The main crop and tillage effects on soil parameters were: β‐glucosidase activity was greater after lupin than after oat, and the opposite was true for the number of culturable fungi. Organic carbon, phosphatase, cellulase and protease were greater in tilled soil than in the absence of tillage. Associations between variables that were stable over the 2 yr were those for mineral N and urease activity, cellulase activity and pH, and that of phosphatase activity and organic C. Our results contrast with most of the previous information on the effect of tillage on soil enzymes, where the activities were reported to be unchanged or decreased following tillage. This difference may be related to the small organic C content of the soil and to the fact that it was under fallow prior to the start of the experiment. In consequence, incorporation of residues would provide new sources of labile organic C for soil microbes, and result in increased enzymatic activity. The results obtained suggest that in coarse‐textured soils poor in organic matter, tillage with residue conservation after a period of fallow rapidly improves several soil characteristics and should be carried out even if it were to be followed by a no‐till system in the following years. This should be taken into consideration by land managers and technical advisers.     

Enzyme activities in semiarid soils under conservation reserve program,native rangeland,and cropland

There is limited knowledge of biochemical processes in low carbon content soils of semiarid regions under different land use and management. This study investigated several enzyme activities of C, N, P, and S transformations in semiarid soils with different clay (10–21 %) and sand (59–85 %) contents that were under conservation reserve program (CRP), native rangeland (NR), and cropland (CL) under sunflowers (Eriophyllum ambiguum (Gray)), continuous cotton (Gossypium hirsutum L.), or in rotations with wheat (Triticum aestivum L.) or sorghum (Sorghum bicolor L.) in West Texas, USA. Soils under CRP and NR showed higher total C and N contents than cultivated soils under continuous cotton, but soil pH (6.7–8.4) was not affected by the management or land use studied. The activities of β‐glucosidase, β‐glucosaminidase, arylamidase, acid and alkaline phosphatase, phosphodiesterase, and arylsulfatase (mg product (kg soil)^–1 h^–1) were lower in CL under continuous cotton compared to cotton in rotation with other crops, CRP, and NR. The enzyme activities were also lower when compared to soils from other regions. Linear regression analyses indicated positive correlations between enzyme activities and total C (r values up to 0.96, P < 0.01). There was a positive relationship between enzyme activities and total N, but soil pH showed the opposite trend. Enzyme activities were significantly intercorrelated with r values up to 0.98 (P < 0.001). The specific enzyme activities (mg product (g organic C)^–1) were lower in continuous cotton in comparison to the uncultivated soils (i.e., NR and CRP) reflecting differences in organic matter quantity and quality due to cultivation. Among the enzymes studied, the specific activities of β‐glucosidase and arylamidase showed a more pronounced decrease with increasing soil depth. In general, soils under CRP or wheat‐cotton rotations revealed higher enzyme activities than soils under the common agricultural practice for these regions, i.e., continuous cotton under conventional tillage.     

Determination of β‐Glucan Molecular Weight Using SEC with Calcofluor Detection in Cereal Extracts

A high‐performance size‐exclusion chromatography system (HPSEC) was set up with detection based on the specific binding of Calcofluor to β‐glucan for determination of amount and molecular weight of β‐glucan in different cereal extracts. To calibrate the HPSEC system, a purified β‐glucan was fractionated into narrow molecular weight ranges and the average molecular weight was determined before analysis on the HPSEC system. The detector response was similar for β‐glucans from oats and barley and appeared to be independent of molecular weight. Four different methods for extraction of β‐glucan from different cereal products were tested: two alkaline, one with hot water and added α‐amylase, and one with water and added xylanase. Inactivation of endogenous β‐glucanase was crucial for the stability of the extracts, even when extracting at high temperature or pH. Yields varied widely between the different extraction methods but average molecular weight and molecular weight distribution were similar. Extraction with sodium hydroxide generally gave a higher yield and molecular weight of β‐glucan in the extracts.     

Enzymic involvement in the biogeochemical responses of a Welsh peatland to a rainfall enhancement manipulation

 Microbial enzyme activities were followed during a field-based experimental simulation of the effects of higher rainfall in a Welsh peatland. The treatment did not significantly affect the activities of the carbon cycling enzymes, β-glucosidase, esterase or xylosidase. In contrast, the activity of the enzyme sulphatase decreased by 44% (P<0.001) in response to the wetter conditions. The manipulation suggests that should climate change cause conditions to become wetter in peatlands, then (with the exception of sulphatase) current levels of wetness may be sufficient to limit decomposition processes, and thus any further increase in wetness is unlikely to induce a further decrease in decomposition rates. Correlations were found between the esterase activity and both nitrous oxide flux (r=–0.44, P<0.05), and methane release (r=0.53, P<0.01). Likewise, there was a correlation between xylosidase activity and both carbon dioxide emission (r=0.52, P<0.01) and aluminium concentration (r=0.58, P<0.01). All of the enzymes correlated positively with dissolved organic carbon (range r=0.53, P<0.01 sulphatase to r=0.61, P<0.001 glucosidase). Together, the correlations lend support to recent hypotheses suggesting that enzymes exert an influence over wetland biogeochemical properties. Received: 29 May 1997