N-acetylmuramic acid 6-phosphate lyases (MurNAc etherases): role in cell wall metabolism, distribution, structure, and mechanism

MurNAc etherases cleave the uniqued-lactyl ether bond of the bacterial cell wall sugar N-acetylmuramic acid (MurNAc). Members of this newly discovered family of enzymes are widely distributed among bacteria and are required to utilize peptidoglycan fragments obtained either from the environment or from the endogenous cell wall (i.e., recycling). MurNAc etherases are strictly dependent on the substrate MurNAc possessing a free reducing end and a phosphoryl group at C6. They carry a single conserved sugar phosphate isomerase/sugar phosphate- binding (SIS) domain to which MurNAc 6-phosphate is bound. Two subunits form an enzymatically active homodimer that structurally resembles the isomerase module of the double-SIS domain protein GlmS, the glucosamine 6-phosphate synthase. Structural comparison provides insights into the two-step lyase-type reaction mechanism of MurNAc etherases: β-elimination of the D-lactic acid substituent proceeds through a 2,3-unsaturated sugar intermediate to which water is subsequently added. Received 31 August 2007; received after revision 12 October 2007; accepted 1 November 2007     

塑料门窗质量影响的因素分析

本文介绍了塑料门窗的加工制作安装过程中各种对门窗质量的影响因素,并进行了分析,结合实际工作经验指出了具体的要求和措施,从而保证了塑料门窗的质量.     

甲酸去除有效氯法改进漂白粉中总钙质量分数的测定

提出用甲酸去除漂白粉中的有效氯后,直接测定漂白粉中总钙质量分数的新方法,研究甲酸用量、反应时间对总钙质量分数测定的影响.用该方法测定了漂白粉中总钙质量分数,甲酸法相对标准偏差为0.072％,测定结果与碘量法一致.     

偶氮氯膦Ⅲ比色法测定褐藻胶中微量钙

作者研究了以偶氮氟膦Ⅲ比色测定褐藻胶中微量钙的方法。在溶液pH为3.0～3.5时,钙与偶氮氯膦Ⅲ形成绿蓝色络合物,络合物最大吸收波长在620nm处,摩尔吸光系数为9.2×10~3。络合物组成为1:1,钙的回收率为98.0～106.0％,可用EDTA或NH_4F、8—羟基喹啉掩蔽铁、铝、锌、镁。本方法可测出褐藻胶中1％以下的钙。     

磷酸酯酰氧基异辛醇铝酸酯（PIA）偶联剂性质的研究

本文报导磷酸酯酰氧基异辛醇铝酸酯（ＰＩＡ）的ＩＲ、２７Ａｌ－ＮＭＲ、ＤＴＡ和水解性等理化性质的测定结果，以及ＰＩＡ改性碳酸钙在液体石蜡中的粘度、填充量、沉降性，及ＰＩＡ适用范围的主要研究结果。     

Mn液中Ca溶解量及第3组元的影响

用密封容器气液平衡法，测定了Ｃａ在Ｍｎ液中的饱和溶解量及第３组元Ｃ、Ｓｉ，Ｎｉ，Ａｌ，Ｃｒ和Ａｓ对其的影响，得到的Ｍｎ液中Ｃａ饱和溶解量与温度的关系式，以及１６７３Ｋ下Ｍｎ液中第３组元与钙的活度相互作用系数。     

尿素对难溶性磷酸盐作用的分析

通过试验得知尿素与磷肥混和施用，土壤中水溶性磷的含量比单施磷肥时要高，表明尿素有活化难溶性磷酸盐的作用．