Abstract
Abstract Transcarboxylase has been isolated from Propionibacterium shermanii grown in the presence of either 60Co or 65Zn, and it has been shown that there is good correlation between radioactivity and enzymatic activity during the final stages of purification. Quantitative determinations of the metal content by atomic absorption analyses indicate that approximately 2 moles of cobalt and 4 moles of zinc are usually present per mole of enzyme (molecular weight 670,000), giving a total metal content which is equimolar with the biotin content of the enzyme. Although the sum of the cobalt and zinc content is constant, the ratio between the two metals has been found to vary. The enzyme causes a substantial broadening of the nuclear magnetic signal arising from the methyl protons of pyruvate. The broadening effect is reversed by increasing concentrations of oxalate. It is proposed that cobalt and zine function at the active site for pyruvate. Radioactivity of 60Co-labeled transcarboxylase is primarily associated with a subunit of the enzyme with a sedimentation constant of 6S that contains little or no biotin.
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