Interpretation of Nonhyperbolic Behavior in Enzymic Systems. I. Differentiation of Model Mechanisms

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Abstract
Mechanistic interpretation of nonhyperbolic rate and binding responses of enzymic reactions involves interlaced distinctions between steady-state and quasi-equilibrium kinetics, between the effects of K, V, and KV types of subunit interactions, and between the effects of different model mechanisms. Therefore (a) the steady-state and quasi-equilibrium predictions of selected kinetic models were analyzed. In most instances the degree of the rate function is a good discriminator between the two types of kinetics. (b) Sensitive detection of K effects in quasi-equilibrium is possible by observing the dependence of the ratio (relative velocity/fractional binding) on the substrate concentration, (c) Relationships between Adair binding constants and constants of models proposed by Pauling, by Monod et al., and by Koshland et al. permit testing the validity of these models to experimental binding data. For illustration the results of Roughton on the binding of oxygen to sheep hemoglobin have been analyzed, which appear to exclude the applicability of models of Pauling and Koshland, but may admit the mechanism of Monod et al. These criteria have been discussed in terms of a general scheme of presently feasible model differentiations.

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