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Enzymatic Degradation of Azaserine^*

( Division of Experimental Chemotherapy, Sloan-Kettering Institute for Cancer Research, and the Sloan-Kettering Division, Cornell University Graduate School of Medical Sciences, New York, N.Y.)

Mouse liver contains an enzyme which rapidly decomposes certain O-esters of L-serine to give pyruvate and ammonia. Kidney, spleen, intestine, and muscle have much lower enzyme activities. The enzyme has a broad pH optimum of around 7.2. It is inhibited by fluoride but not by versene, dithizone, or cyanide. The K_m for azaserine is 2.3–2.4 · 10^-3 M at pH 7.3–7.4. The best substrates for the enzyme are O-esters of serine in which the terminal groups on the acid moiety are relatively nonionized. The reaction mechanism is probably an ,ß elimination which gives the acid, pyruvate, and ammonia as end-products.

^* This work was supported by grants T36 and T37 from the American Cancer Society and by CCNSC contract #SA-43-ph-2445 and Training grant #5015, National Cancer Institute, Public Health Service.

Received 7/20/61.