Distribution and properties of lactate dehydrogenase isoenzymes in red and white muscle of freshwater fish

The distribution and kinetics of LDH isoenzymes in red and white muscles of 5 species of salmonids, 4 species of cyprinids and one coregonid species were studied. In all species the white muscles are characterized by the occurrence of only the most cathodic isoenzymes, or groups of isoenzymes. The red muscles contained either the full set of isoenzymes (cyprinids) or a selection in which the anodic forms dominated (salmonids, coregonid). The most striking difference between the two types of muscle was met inCoregonus sp. The temperature profiles of pyruvate affinity are similar in all species of fish studied. On the other hand, K_m(pyr) values and degree of pyruvate inhibition are closely related and vary greatly with temperature, with the taxonomic position (and thus biology) of the species, and with electrophoresic mobility of the isoenzyme. Highest affinity and strongest inhibition occurred in the anodic (H₄) isoenzymes of cyprinids at low temperature; lowest affinity and zero inhibition in the cathodic isoenzymes (M₄ M₄) of salmonids and coregonids at high temperature. In salmonids the more recently duplicated loci of the M-group of isoenzymes possess identical K_m values at all temperatures, whereas the two older M and H loci differ greatly in this respect. Thus the more recent duplication of LDH loci in salmonids and coregonids may be seen as a mechanism by which the tetramers required for LDH activity can be constructed from more closely related subunits than are provided by the older M and H loci.Some problems in connection with the determination of the kinetic constants of the lactate oxidase reaction are discussed and it is suggested that an alkaline, pyruvate trapping system provides conditions which are more realistic than those of other assay systems. The K_m(lactate) values found are in the biological range and, at 20°C, provide further circumstantial evidence that the red muscles of fish should be capable of oxidizing the lactate produced by the white muscles during strenuous exercise. At 4°C the K_m(lactate) values are abnormally high in all muscle preparations and thus are not correlated with the K_m(pyruvate) values which are lowest at this temperature.     

杂交水稻氮素代谢特性的研究(英文)

研究结果表明,在分蘖、孕穗和抽穗期,供试杂交稻组合的功能叶片中的氮浓度、可溶性蛋白质和叶绿素含量明显高于常规稻.在其氮素代谢过程中,NR,GS,Fd-GOGAT,GPT和GOT酶活力,在供试品种间的差异是:汕优64>汕优6号>浙丽1号>秀水48,氮素营养条件的变化对此差异无影响,在杂变稻与常规稻之间,Fd-GOGAT酶活力和NR酶活力差异最大(分别达到50～70％和40～70％),而GPT酶活的差异较小.结果还表明,在不同水稻品种的功能叶中,上述5种酶的活力,与叶中可溶性蛋白质含量及全氮量均呈积显著正相关,这说明在杂交稻叶片中,氮素同化和蛋白质合成的酶系统,其活力优于常规稻的该酶系统,它们是杂交稻吸收利用氮素能力强的重要生理基础之一.     

不同烤烟品种成熟期碳氮代谢关键酶活性的变化

为了明确南雄烟区主栽烤烟品种碳氮代谢规律,以烤烟品种粤烟97、粤烟98和K326为材料,研究了不同烤烟品种成熟期碳氮代谢关键酶活性的变化。结果表明:随着烟叶的成熟,各烤烟品种烟叶总叶绿素含量、硝酸还原酶活性、转化酶活性均表现为下降的趋势,淀粉酶活性呈先升高后下降的趋势;成熟前期粤烟98总叶绿素含量较高,粤烟97总叶绿素含量较低,但粤烟98叶绿素降解速率较快,粤烟97叶绿素降解速率较慢;成熟前期K326和粤烟98的硝酸还原酶活性极显著高于粤烟97,整个成熟期各烤烟品种间转化酶活性和淀粉酶活性差异不显著。总的来看,粤烟98碳氮代谢协调性相对较好。     

烤田对土壤中氮素和与氮有关的酶活性影响

在水稻分蘖期对5种不同尿素氮肥水平的小区进行烤田5天的试验。试验结果表明,在烤田过程中,脲酶活性变化不明显,呈微弱增加趋势。硝酸还原酶活性急剧降低,羟胺还原酶活性呈波动变化,几乎检测不到亚硝酸还原酶活性。土表的铵态氮也呈波动变化,随着烤田时间的增加铵态氮含量降低。土表的硝态氮浓度不断增加,烤田增大了复水后硝态氮向地下水淋溶的趋势。施氮量越多,土表的矿质氮含量也越多。土壤烤田的主要目的是通过降低土壤的含水量,提高土壤的氧化还原电位,改善土壤的通气状况。     

Effects of nitrogen deposition on growth and survival of montane Racomitrium lanuginosum heath

Montane heaths dominated by the moss Racomitrium lanuginosum are in decline, for which increased atmospheric nitrogen (N) deposition may be partially responsible. To test this, field plots in northeast Scotland were treated with either low or high (10 or 40 kg N ha⁻¹year⁻¹) doses of nitrogen (as NO₃⁻ or NH₄⁺) for 2 years. Although Racomitrium tissue N increased after treatment, with greater response for low than high N application, activity of the enzyme nitrate reductase and Racomitrium growth were severely inhibited by increasing N addition. Racomitrium cover declined following N addition and graminoid cover increased, also with greatest effect at high doses. Of all measurements, only nitrate reductase showed a distinction between NO₃⁻ and NH₄⁺ application. The results demonstrate the detrimental effects of even low increases in nitrogen deposition on the moss heath, suggesting that loss of Racomitrium and its replacement by graminoids is strongly linked to increased levels of anthropogenic N pollution.     

Selection and evaluation of nitrate-tolerant strains of Rhizobium leguminosarum biovar viceae specific to the lentil

Seventeen strains of Rhizobium leguminosarum biovar viceae specific to the lentil (Lens culinaris L.) were screened, using the high-yielding lentil cultivar L 4076, for their tolerance to three levels of NO _inf3 ^sup- : 0, 4, and 8 mM NO _inf3 ^sup- . Preliminary screening of this symbiosis for nodulation and N fixation in the presence of NO _inf3 ^sup- showed significant variations among the strains. The number of nodules decreased and nitrogenase activity was depressed in all strains in the presence of NO _inf3 ^sup- . Strains L-1-87, L-27-89, L-33-89, and L-40-89 tolerated 8 mM NO _inf3 ^sup- . Four strains, three tolerant of NO _inf3 ^sup- (L-1-87, L-27-89, and L-33-89), and one sensitive (L-11-89) to NO _inf3 ^sup- , were selected from preliminary screening and used in a pot experiment to assess the symbiosis in the presence of 6 mM NO _inf3 ^sup- at three stages of plant growth, viz., 40 days, 60 days, and at the final harvest. In general, the weight of nodules and C₂H₂ reduction activity was significantly higher after 60 days than after 40 days. Inoculation with strain L-1-87 produced the maximum number of nodules, and root and shoot biomass both in the presence and the absence of NO _inf3 ^sup- . Nitrate reductase activity in the tops and nodules was assayed only after 60 days and did not show significant variations among strains and NO _inf3 ^sup- treatments. The grain yields for all strains except L-11-89 were significantly higher in the presence of NO _inf3 ^sup- than in the absence of NO _inf3 ^sup- , indicating that tolerant strains contributed symbiotically fixed N to the plant's N pool, resulting in an additive effect on yield. Inoculation with strain L-1-87 produced the maximum grain yield and this strain appears to have potential use as an inoculant in the presence of high levels of soil N.     

Hypolipemic and hypoglycaemic activity of bergamot polyphenols: From animal models to human studies

Bergamot juice produces hypolipemic activity in rats though the mechanism remains unclear. Here we investigated on the effect of bergamot extract (BPF) in diet-induced hyperlipemia in Wistar rats and in 237 patients suffering from hyperlipemia either associated or not with hyperglycaemia. BPF, given orally for 30 days to both rats and patients, reduces total and LDL cholesterol levels (an effect accompanied by elevation of cHDL), triglyceride levels and by a significant decrease in blood glucose. Moreover, BPF inhibited HMG-CoA reductase activity and enhanced reactive vasodilation thus representing an efficient phytotherapeutic approach in combating hyperlipemic and hyperglycaemic disorders.     

树木硝酸还原酶的研究概况与应用前景

树木硝酸还原酶（NR）在林木生长中的作用越来越为人们所认识和重视。本文综述了树木NR研究的动态，讨论了NR在林业生产上的应用前景，分析了NR作为树木性状预测的生化指标的理论根据和应用领域，并根据当前树木NR研究的发展趋势，结合我国林业生产上的问题，提出了加快我国树木NR应用研究进展的建议。     

茶树花色素还原酶基因的克隆与原核表达

采用RACE技术,从茶树新品系"1005"的嫩芽中克隆出ANR基因的全长cDNA(1260 bp),其推导的氨基酸序列与茶树、葡萄花色素还原酶的一致性分别为99%和84%;并成功构建了ANR基因的原核表达载体pET-ANR,在大肠杆菌BL21中表达出预期大小(约45 ku)的融合蛋白.     

猕猴桃果实L-半乳糖内酯脱氢酶和脱氢抗坏血酸还原酶cDNA片段的克隆与序列分析

克隆猕猴桃果实L-半乳糖内酯脱氢酶(GalLDH)和脱氢抗坏血酸还原酶(DHAR)基因,可为揭示猕猴桃高抗坏血酸(AsA)含量的分子机制奠定基础。研究以猕猴桃果实为材料提取总RNA,采用RT-PCR法,克隆出L-GalLDH基因的cDNA片段857 bp和DHAR基因的cDNA片段594 bp并测序,根据测序结果推测其氨基酸序列,并与刺梨、拟南芥、花椰菜、甘薯和草莓等植物的GalLDH基因和DHAR基因氨基酸序列进行亲缘分析。结果表明,猕猴桃GalLDH基因氨基酸序列和核苷酸序列与刺梨的相似性高达88%,其在同源基因进化关系树中单独聚为一类;DHAR基因氨基酸序列和核苷酸序列与苹果的相似性高达98%和99%,两者在进化关系上聚为一类。可知克隆到的2个核苷酸片段确为猕猴桃L-GalLDH和DHAR基因cDNA片段,同源基因植物亲缘关系聚类与传统的形态分类有一定的差异。