期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1972
卷号：69
期号：9
页码：2417-2419
DOI：10.1073/pnas.69.9.2417
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The kinetics of the reaction catalyzed by egg-white lysozyme from hen eggs (EC 3.2.1.17 ) was investigated by measurement of the decrease in turbidity of suspensions of dried Micrococcus luteus cells. The substrate and NaCl concentration were varied, as well as the hydrostatic pressure (1-476 atm). A plot of the initial velocity against the reciprocal of the substrate concentration gave straight lines. From these plots values for the maximum velocity, V, and the apparent Michaelis constant, Km, as well as the effect of NaCl concentration were determined. The maximum velocity showed a pronounced maximum when plotted over a range of NaCl concentration from 0-0.208 M. The volume change of activation, {Delta}V[unk], calculated from V, was negative, and decreased in absolute value from -8 to about 0 cm3/mol as the NaCl molarity was increased over the above range. This effect is explained as due to a different number of salt molecules being built into activated complexes with each of these activated complexes reacting at its own characteristic rate. Strong pressure-dependence of enzyme catalysis indicates appreciable conformational changes of the enzyme as it is incorporated into the activated complex. The volume change causing the pressure effect arises principally from changes in the number of ionized species with the accompanying electrostriction.
关键词：volume change of activation ; enzyme conformation ; electrostriction ; absolute reaction rate theory
