Studies on carboxylases. XI.- Enzymatic inhibition of pyruvic carboxylase by the penicillins and other antibiotics not included in the groups already studied

Abstract

Continuing the study of enzymatic inhibition of pyruvic carboxylase by antibiotics of therapeutic importance the penicillins and other antibiotics not included in the groups previously dealt with were studied.

For the penicillins, it is observed in the first place that there is no difference between the sodium and potassium salts. Secondly, substrate concentration has an influence on the amount of inhibition. Application of the principales of Lineweaver and Burk, and graphical representation of v/v, against the concentration of inhibitor suggests that penicillin forms with the enzyme complexes in which the relative proportions are two molecules of antibiotic for one of enzyme. Inactive penicillin is even more inhibiting than the active form. The addition of inert globular proteins (ovoalbumin, seroglobulin, etc.) does not reduce inhibition which indicates a certain specificity of action. Addition of cysteine does not reduce inhibition which indicates that the interaction is not with the sulphydryl groups of the enzyme. Diethyl-amino-ethilye ester is less inhibiting and the inhibition responds to a mechanism evidently different from that which corresponds to penicillin G.

Framycetin inhibits through a complex mechanism. Fumagillin and fungicidin have no marked action on the enzyme which is object of our study; the same applies to neo-flavoricin.