SIGNIFICANCE OF INTERMEDIARY PLATEAU REGIONS IN ENZYME SATURATION CURVES

An investigation has been made of the catalytic and binding parameters required to generate kinetic saturation curves possessing an intermediary plateau region. General rate equations were derived for the case in which the rate of equilibration between substrate and enzyme is rapid relative to the rate of catalysis. Analysis of the second derivative of these expressions revealed that kinetic or binding curves with pronounced intermediary plateau regions will only be produced when (1) the enzyme or enzymes present possess a total of more than two substrate binding sites and (2) the relative magnitude of the intrinsic catalytic or binding constants of these sites first decreases, then increases as the enzyme is saturated. Multisite enzymes will not yield these undulating kinetic curves when their intrinsic catalytic, or binding constants progressively increase, progressively decrease or remain constant with saturation. Applying these and other diagnostic criteria, certain enzyme models could be unequivocably excluded as possible explanations for the complex kinetic curves experimentally observed. © 1969, American Chemical Society. All rights reserved.