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Extracellular enzymatic activities in soils are essential for the cycling of organic matter. These activities take place in multiphase environments where solid phases profoundly affect biocatalytic activities. Aspergillus niger is ubiquitous in soils; its β-glucosidase plays an important role in the degradation of cellulose, and therefore in the global carbon cycle and in the turnover of soil organic matter. However, the information on the interactions of this protein with soil minerals is very limited, and even less is known about their consequences for the hydrolysis of the natural substrate cellobiose. We therefore characterised the sorptive interactions of this enzyme with the soil minerals montmorillonite, kaolinite and goethite and quantified the resulting changes in the hydrolysis rate of cellobiose. Fractions of adsorbed protein, and the resulting catalytic activity loss, were lower for montmorillonite than for kaolinite and goethite at given experimental conditions; adsorption was 9.7 ± 7.3% for montmorillonite, 70.3 ± 3.1% for kaolinite and 71.4 ± 1.8% for goethite, respectively. Adsorption of the protein to the minerals caused a total decrease in the catalytic activity of 18.8 ± 3.4% for kaolinite and 17.9 ± 4.7% for goethite whereas it was not significant for montmorillonite. The average catalytic activity lost by the pool of adsorbed molecules was 26.8% for kaolinite and 25.0% for goethite. Both the amount of adsorbed protein and the resulting loss of catalytic activity were found to be independent of the specific surface areas yet were influenced by the electrical properties of the mineral surfaces. Under the experimental conditions, montmorillonite and kaolinite are negatively charged whereas goethite is positively charged. However, because of the adsorption of phosphate anions from the buffer, a charge reversal took place at the surface of goethite. This was confirmed by zeta (ζ)-potential measurements in phosphate buffer, revealing negative values for all the tested minerals. Indeed goethite interacted with the enzyme as a negatively charged surface: the amount of adsorbed protein and the resulting catalytic activity loss were very similar to those of kaolinite. Our results show that, even if an important fraction of β-glucosidase is adsorbed to the minerals, the catalytic activity is largely retained. We suggest that this strong activity retention in presence of soil minerals results from a selective pressure on A. niger, which benefits from the activity of the adsorbed, and thus stabilized, enzyme pool. 相似文献
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土各粒级K+吸附特征有很大区别.在一定平衡液浓度下,颗粒越细,土壤固相吸附量越大,不同粒级固相吸附量大小顺序是(<0.1m)>(<1m)>(1~2m)>(2~5m),不同粒级土壤有效阳离子交换量也具有相同的变化规律.混合样中不同粒级组分对吸附的贡献可用吸附贡献率表示,土各粒级饱和吸附贡献率大小顺序为(<1m)>(1~2m)>(>5m)>(2~5m),其中粘粒部分的饱和吸附贡献率为85%左右.在供试混合土样中<1m粒级吸附贡献率随平衡液浓度增大呈幂函数形式增大,相反,1~2m、2~5m粒级吸附贡献率随平衡液浓度增大则呈幂函数形式减小.实验证明混合样中不同粒级K+吸附存在交互作用,吸附交互作用大小可用吸附交互作用系数表征,<1m和1~2m之间存在吸附负交互作用,且随平衡液浓度增大而增强.<1m和2~5m之间存在吸附正交互作用,且随平衡液浓度增大而减弱.论述了建立土壤多粒级组分吸附方程的必要性,提出了多粒级组分吸附方程q=ρ(c)rifi(c) 相似文献
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从观察现象出发,经理论分析旋转气流所产生的使茎秆、穗头向滚筒贴附的作用,揭示了该作用与板齿结构和运动参数间的关系,并对环流流场的流速、压头的形成亦进行了分析。实验测定结果,基本验证了这些关系 相似文献
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Laboratory incubation studies were conducted to determine the dynamics of low-molecular-weight aliphatic carboxylic acids and their anions (LACAs) and respiration in three soils incorporated with five types of plant residues differing in chemical composition. Concentrations of total and individual LACAs in soils decreased sharply with initial 3 days after addition of plant residues, and varied with types of plant residue and soil. Irrespective of soil types, the amount of total extractable LACAs was highest in the soils treated with chickpea, followed by lucerne and high-N wheat straw, and lowest with low-N wheat straw. Lancelin soil [initial pH(CaCl2) 5.06] contained higher concentration of extractable LACAs compared with Bodallin (pH 4.54) and Wodjil soil (pH 3.87). Soil respiration rate was rapidly increased by the addition of plant residues, and reached the peak by Day 3. Respiration rate was the greatest in Lancelin soil and the smallest in Wodjil soil. The amounts of CO2 respired over 7 days were equivalent to 6-25% of the added C for Wodjil soil, 6-39% for Bodallin soil and 6-47% for Lancelin soil, depending on type of plant residue. Those amounts over 105 days increased further. Irrespective of plant residue and soil type, the cumulative respiration correlated positively with concentrations of N, excess cations and soluble C in plant residues and initial soil pH, and negatively with C:N of plant residues. The results suggest that chemical composition of plant residues plays an important role at the initial stage of residue decomposition. 相似文献
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邻苯二甲酸和水杨酸在可变电荷土壤中的吸附行为 总被引:3,自引:1,他引:3
研究了2种低分子量有机酸邻苯二甲酸和水杨酸在2种代表性可变电荷土壤红壤和砖红壤中的吸附行为。结果表明,可变电荷土壤对有机酸的吸附容量较大,对邻苯二甲酸的吸附亲和力大于对水杨酸的亲和力,在砖红壤中2种有机酸的吸附量大于在红壤中的,这与土壤的游离铁、铝氧化物的含量一致。土壤氧化铁在有机酸吸附中起着重要作用,粘土矿物如高岭石对有机酸的吸附量很小。有机酸的吸附涉及专性吸附和静电吸附2种机制,并以前者为主。当pH小于4.5时,pH的改变对有机酸的吸附影响不大;当pH大于4.5时,有机酸的吸附量随pH的增加而减小。 相似文献