Rao K S, Rajendran S, Rajeshwara A N, Prakash V
Food Chemistry Department, Central Food Technological Research Institute, Mysore, India.
J Protein Chem. 1991 Jun;10(3):291-9. doi: 10.1007/BF01025628.
The present investigation shows the effect of alkaline pH on the structure-function relationship of lipase from wheat germ. There is a 70% decrease in lipase activity at pH 10.0, which decreases to 93% at pH 12.0 as compared to neutral pH activity (Rajendran et al. 1990). This change is shown to be as a result of loss of alpha-helical structure with a concomitant increase in aperiodic structure. The results with fluorescence spectra and tyrosyl ionization indicate gradual exposure of aromatic side chains of tyrosine and tryptophan to the bulk solvent along with the structural changes. The enzyme is in an extended form at alkaline pH with a volume change of - 1300 ml mol as also indicated by increase in reduced viscosity to 12.5 ml g and significant decrease in sedimentation coefficient. The kinetics of the reaction points to a cooperative pseudo first-order reaction as determined by stopped-flow kinetic analysis in the ultraviolet region. The inactivation mechanism appears to follow a two-step mechanism of a fast and a slow reaction.
本研究显示了碱性pH对小麦胚芽脂肪酶结构-功能关系的影响。与中性pH活性相比，在pH 10.0时脂肪酶活性降低70%，在pH 12.0时降至93%（拉金德兰等人，1990年）。这种变化表现为α-螺旋结构丧失，同时无规结构增加。荧光光谱和酪氨酸离子化的结果表明，随着结构变化，酪氨酸和色氨酸的芳香侧链逐渐暴露于大量溶剂中。在碱性pH下，该酶呈伸展形式，体积变化为-1300 ml/mol，这也由比浓粘度增加至12.5 ml/g和沉降系数显著降低所表明。反应动力学表明这是一个协同假一级反应，这是通过紫外区域的停流动力学分析确定的。失活机制似乎遵循快速和缓慢反应的两步机制。
