l -SERINE SPECIFIC DEHYDRASE FROM CLOSTRIDIUM ACIDI-URICI

Abstract

Concentration by protamine and ammonium sulfate fractionations (giving an 8-fold increase in specific activity) showed this enzyme to require a strongly reducing environment and a divalent metal (best satisfied by ferrous iron) for maximal activity. Complete inhibition was obtained with sulfhydryl-binding reagents and metal-chelating agents. A requirement for pyridoxal phosphate as a co-factor could not be demonstrated. Treatment with hydroxylamine or semicarbazide failed to decrease the rate of serine deamination, and the activity of the enzyme so treated was not enhanced by addition of pyridoxal phosphate. The pH optimum was found to be between 8 and 8.4, and the Km value for L-serine was determined to be 2.4 x 10-3 M. The enzyme showed no detectable activity on L-cysteine or L-threoine, nor did these compounds decrease the rate of L-serine deamination. The maximal dehydrase activity of crude extracts was comparable with the over-all rate of uric acid fermentation by this organism and is compatible with serine serving as an intermediate in the degradation of purines.