Kinetics of enzymes with iso-mechanisms: analysis of product inhibition.
Kinetics of enzymes with iso-mechanisms: analysis of product inhibition.
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具有异构机制的酶动力学：产物抑制分析。
DOI：
10.1042/bj2960355
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发表时间：
1993
期刊：
影响因子：
--
通讯作者：
Northrop,DB
中科院分区：
文献类型：
--
作者：
Rebholz,KL;Northrop,DB
当异构化部分限速时，可以在产物抑制的动力学模式中检测到游离酶的异构化。由于底物和产物与不同形式的游离酶的结合，动力学模式是非竞争性的。这会在速率方程中添加一个附加项，有时表示为 KSP。一些动力学家指出，随着异构化速率相对于催化转化率变高，拦截效应将变小，KSP 将接近无穷大，并且该模式将看起来具有竞争力。布里顿[(1973)生物化学。 J. 133, 255-261]断言，当异构化率变低时，KSP也将接近无穷大。第二个断言是不正确的，可以追溯到用于检查 KSP 作为相对速率常数函数的特定模型和图形表示。 KSP 的函数被描绘为具有两个根的抛物线，而实际上是一条具有一个根的直线。证明二次方根成立的代数条件在反应速率为零的极限内获得，因此与实验无关，并且仅基于 KSP 的竞争性抑制的出现是无效的。使用更通用的模型，推导并提出了新的方程，当异构化平衡接近 1 时，可以根据产物抑制数据直接计算游离酶异构化的表观速率常数，以及当大于或小于 1 时速率常数的有用限制。
Isomerizations of free enzyme can be detected in kinetic patterns of product inhibition when the isomerization is partially rate-limiting. The kinetic pattern is non-competitive, owing to binding of substrate and product to different forms of free enzyme. This adds an additional term to the rate equation, sometimes represented as KSP. Several kineticists have noted that, as the rate of isomerization becomes high in relation to catalytic turnover, the intercept effect will become small, KSP will approach infinity, and the pattern will look competitive. Britton [(1973) Biochem. J. 133, 255-261] asserted that KSP will also approach infinity when the rate of isomerization becomes low. This second assertion is incorrect and can be traced to the particular model and graphical representation used to examine KSP as a function of relative rate constants. The function portrayed as a parabola with two roots for KSP is, instead, a straight line with one root. The algebraic condition justifying the second root obtains in the limit of zero in the rate of reaction and thus is not experimentally relevant, and the appearance of competitive inhibition, based on KSP alone, is not valid. Using a more general model, new equations are derived and presented which provide direct calculations of the apparent rate constants for free enzyme isomerizations from product-inhibition data when the equilibrium of the isomerization is near 1, and useful limits for the rate constants when greater than or less than 1.