A study of the inhibition of the catalytic action of L-amino acid oxidase

Abstract

The inhibition of the catalytic action of L-amino acid oxidase by salicylic and benzoic acids was studied over a pH range of 5.7 to 7.7 using standard manometric techniques. L-leucine, L-methionine, and L-phenylalanine were used as substrate. In order to explain the data obtained, it was postulated that the total amount of enzyme in solution was almost completely associated with either the substrate or the inhibitor and the rate of reoxidation was much greater than the rate of reduction of the enzyme. The kinetic expression derived from these two postulates involved the ratio of the constants of association of the enzyme-inhibitor complex to the enzyme-substrate complex, K[subscript i]/K[subscript s], which could not be separated using the data obtained. From the pH dependence study it was determined that the inhibition increased with a decrease in pH as the square of the hydrogen ion concentration. Since K[subscript i]/K[subscript s] could not be separated, it could not be determined in which process this effect was involved. From a temperature dependence study of the inhibition, the difference in the enthalpies of formation of the two complexes was determined.