Crystal structure of the Y52F/Y73F double mutant of phospholipase A2: increased hydrophobic interactions of the phenyl groups compensate for the disrupted hydrogen bonds of the tyrosines.

The enzyme phospholipase A2 (PLA2) catalyzes the hydrolysis of the sn-2 ester bond of membrane phospholipids. The highly conserved Tyr residues 52 and 73 in the enzyme form hydrogen bonds to the carboxylate group of the catalytic Asp-99. These hydrogen bonds were initially regarded as essential for the interfacial recognition and the stability of the overall catalytic network. The elimination of the hydrogen bonds involving the phenolic hydroxyl groups of the Tyr-52 and -73 by changing them to Phe lowered the stability but did not significantly affect the catalytic activity of the enzyme. The X-ray crystal structure of the double mutant Y52F/Y73F has been determined at 1.93 A resolution to study the effect of the mutation on the structure. The crystals are trigonal, space group P3(1)21, with cell parameters a = b = 46.3 A and c = 102.95 A. Intensity data were collected on a Siemens area detector, 8,024 reflections were unique with an R(sym) of 4.5% out of a total of 27,203. The structure was refined using all the unique reflections by XPLOR to a final R-factor of 18.6% for 955 protein atoms, 91 water molecules, and 1 calcium ion. The root mean square deviation for the alpha-carbon atoms between the double mutant and wild type was 0.56 A. The crystal structure revealed that four hydrogen bonds were lost in the catalytic network; three involving the tyrosines and one involving Pro-68. However, the hydrogen bonds of the catalytic triad, His-48, Asp-99, and the catalytic water, are retained. There is no additional solvent molecule at the active site to replace the missing hydroxyl groups; instead, the replacement of the phenolic OH groups by H atoms draws the Phe residues closer to the neighboring residues compared to wild type; Phe-52 moves toward His-48 and Asp-99 of the catalytic diad, and Phe-73 moves toward Met-8, both by about 0.5 A. The closing of the voids left by the OH groups increases the hydrophobic interactions compensating for the lost hydrogen bonds. The conservation of the triad hydrogen bonds and the stabilization of the active site by the increased hydrophobic interactions could explain why the double mutant has activity similar to wild type. The results indicate that the aspartyl carboxylate group of the catalytic triad can function alone without additional support from the hydrogen bonds of the two Tyr residues.     

A general approach toward the design of inhibitors of serine proteinases: inhibition of human leukocyte elastase by substituted dihydrouracils

A general approach toward the rational design of potential inhibitors of serine proteinases is described. The approach is exemplified and validated through the use of appropriate heterocyclic systems in inhibiting human leukocytes elastase (HLE).     

羊蹄甲属植物种子的裂解色谱鉴定法研究

本文探索了裂解气相色谱法作为植物种子分类表征方法的可能性。对豆科植物中不同属、不同亚属及相同亚属的共10种种子的裂解色谱图,用分区编码法进行区别,分析结果表明,不同种子最少有一个编码不同,方法简易快速,可为高等植物种子的区分提供一种佐证手段。     

黄根豆的核型分析

本文首次对单种属植物黄根豆(Chrysoirhiza adenotricha T.Chen)进行了核型分析,其核型公式为K(2n)=22=22m,并确认黄根豆属(Chrysorhiza)的染色体基数为X=11。     

六种鱼腥藻在大量培养中的生产率和适应性与营养成分比较

连续两年对鱼腥藻的六个品系进行了大量培养比较研究,在长江中下游气候条件下,HB1042和HB1105具有稳定的生产性能,5月下旬至九月中旬123d内,平均有效生长分别为114和100d;其次是HB1058,HB686和HB1017,平均有效生长天分别为73,58和71d;HB13适应性较差。生物量生产率在5月下旬、6月中旬至9月中旬较高,除HB13外,平均都在10g干重/m~2/d以上或接近10g/m~2/d。在不同的季节它们表现出了各自的最高生物量生产率。据此,提出了逐月逐旬采取藻种搭配生产,以获得最高生物量生产率的配合关系。营养成分分析表明它们的蛋白质含量在40％左右;氨基酸组成合理,除某些种类的含硫氨基酸略低外,都符合FAO/WHO的标准。     

鲥鱼的驯养与生物学研究Ⅰ.O+龄幼鱼的生长与食性

本文主要描述池塘养殖条件下鲥鱼幼鱼的生长与食性。1)1987-1989年8月至11月幼鱼生长迅速,快于同期珠江天然个体的生长速度;2)体长26.6-94.9mm的幼鱼主要摄食浮游动物,轮虫和浮游植物出现率随个体增大而减少。食物共有18个属种,摄食频度为100%;3)幼鱼的平均饱满指数为75.70‰。各类食物重量百分比的顺序为:桡足类>枝角类>无节幼体>虾类溞状幼体>轮虫>藻类。     

脂质过氧化对人红细胞膜脂流动性的影响

研究枯稀过氧化氢/高铁血红素体系所产生的烷基过氧自由基对红细胞的损伤。测定了脂质过氧化的产物——丙二脂的生成,并证明阿魏酸钠对脂质过氧化的抑制。荧光偏振的结果指出,膜脂过氧化以后降低了膜脂的流动性。人红细胞用5DSA和16DSA标记并用ESR检测膜脂流动性,结果表明,序参数S几乎没有发生变化,旋转相关时间τ值的增加证明膜脂过氧化以后,疏水尾部的物理状态发生了改变。经脂质过氧化以后,红细胞膜中的不饱和脂防酸的减少,可能是降低膜脂流动性的原因之一。     

大斑啄木鸟取食行为的研究

大斑啄木鸟(Dendrocopos major)是左家地区的常见鸟类,对它的研究,国内有过一些报道。1990年4—5月,笔者对它的取食行为做了较为系统的观察,现整理报道如下。