On the distinction between binding of substrate and kinetic order of addition in enzyme-catalyzed reactions

✍ Scribed by Thomas I. Diamondstone

• Publisher: Elsevier Science
• Year: 1969
• Tongue: English
• Weight: 639 KB
• Volume: 25
• Category: Article
• ISSN: 0022-5193
• DOI: 10.1016/s0022-5193(69)80025-1

✦ Synopsis

An examination of the available data for the rate of formation of enzymesubstrate complexes shows that for enzymes possessing a sequential ordered mechanism the rate constants for the formation of the various complexes (EA, etc.) are on the average two to three orders of magnitude lower than the value of 109 M -1 sec -1 for the lower limit for a diffusioncontrolled process as calculated by Eigen & Hammes (1963). These observations are utilized to derive a rate expression, based on a two-step construction--a binding step and a transformation step--for each enzyme-substrate complex (e.g. E q-A ~ AE ~ EA for the formation of EA), which is identical in form to the expression derived from the simpler conventional mechanism. It turns out that under ordinary conditions the kinetically determined order of addition is formally independent of the physical order of binding substrates. Further, it is shown that these observations are consistent with Koshland's notion of the "induced fit" caused by combination of enzyme and substrate.