Active site directed effectors of allosteric enzymes.

This communication introduces the concept of an active site directed effector, in terms of the two state model of Monod et al. (Monod, J., Wyman, J. and Changeux, J.-P. (1965) J. Mol. Biol. 12, 88-118), a consideration made necessary by the observation that the activity of a number of enzymes of the control type is modulated by effector molecules whose structure is similar to that of the substrate. We present equations which describe the kinetic responses obtained in its absence; this seemingly paradoxical activation, at low (S), is not tions the v versus (S) plot obtained in the presence of the effector crosses that obtained in its absence; this seemingly paradoxial activation, at low (S), is not explainable by the other frequently used two state models (Monod, J., Wyman, J. and Changeux, J.-P. (1965) J. Mol. Biol. 12, 88-118; Rubin, M.M. and Changeux, J.-P. (1966) J. Mol. Biol. 21, 265-274; Frieden, C. (1967) J. Biol. Chem. 242, 4045-4052; Dalziel, K. (1968) FEBS Lett. 1, 346-348 and Nichol, L.W., O'Dea, K. and Baghurst, P.A. (1972) J. Theor. Biol. 34, 255-263). The model is discussed using examples taken from the literature and successfully used to reanalyse published data on the enzyme deoxythymidine diphosphate D-glucose pyrophosphorylase (Frieden, C. (1967) J. Biol. Chem. 242, 4045-4052).