ENZYMATIC-REACTION RATE LIMITS WITH CONSTRAINTS ON EQUILIBRIUM-CONSTANTS AND EXPERIMENTAL PARAMETERS

A general methodology is presented for estimating maximum rates of enz ymatic reactions based on general characteristics of enzymatic reactio n mechanisms, kinetic limits and thermodynamics. The useful range of e xperimentally derived kinetic parameters can also be extended by the m ethodology. The methodology divides the reaction mechanism into physic al and chemical steps. Maximum rates that comply with kinetic and ther modynamic constraints are calculated by setting the physical rate cons tants to their diffusion limits and optimising the chemical rate const ants subject to constraints of the reaction mechanism and overall equi librium constant. Rate estimates from this methodology can be subject to additional constraints from experimental data, and thus conform to the distinctive features of the enzymatic reaction. The methodology is demonstrated using a reversible enzymatic reaction model involving or dered binding of two reactants and ordered release of two products (bi -bi mechanism). Numerical results are shown for alcohol dehydrogenase (EC 1.1.1.1), which has abi-bi mechanism. Pyrophosphatase (EC 3.6.1.1) with a uni-bi mechanism and triosephosphate isomerase (EC 5.3.1.1) wi th a uni-uni mechanism are also examined: (C) 1998 Elsevier Science Ir eland Ltd. All rights reserved.