Abstract
An “Imaginary Reaction Box” (IR Box) was constructed using a microcomputer to elucidate the inhibition mechanisms of δ-aminolevulinic acid dehydratase (ALAD). The IR Box could print out the changes of the concentrations of enzyme, substrate, enzyme-substrate complex and various other components in an enzyme reaction when the amounts of enzyme, substrate, and inhibitor, and provisional velocity constants were input from the keyboard. By using this IR Box, the inhibition effects of Zn, Pb and Hg on ALAD were examined. It was assumed that these metals and ALAD form an active site inhibitor-enzyme complex (EI), an allosteric inhibitor-enzyme complex (IE), an allosteric inhibitor-enzyme-substrate complex (IES), and an allosteric inhibitor-enzyme-active site inhibitor complex (IEI), and that reactions of about 20 kinds occur in the IR Box, including reverse reactions. Results of the reactions in the IR Box made it clear that there are reaction mechanisms which explain the conflicting results obtained from inhibition by these metals in vitro. The IR Box can be a useful tool not only for the investigation of enzyme reactions in vivo which do not obey Michaelis-Menten kinetics, e. g., allosteric regulation and allosteric inhibition, but also for the improvement of the efficiency of experiments involving such reactions.
