S-adenosylmethionine decarboxylase from human placenta.

1. S-adenosylmethionine decarboxylase from human placenta has been purified more than 1200-fold by use of Chromatographic techniques. 2. The molecular weight was determined as approx 53,000 by gel nitration. 3. The enzyme preparations were quite unstable in the absence of reducing agents; the crude enzyme was rapidly inactivated at 4°C whereas after the DEAE-cellulose step it was moderately stable. 4. Putrescine, cadaverine, 1,6-diamino-n-hexane stimulated the reaction rate whereas the enzyme was completely insensitive to spermidine. The apparent activation constant for putrescine was estimated to be 0.25 mM at a substrate concentration of 0.03 mM. 5. The apparent Km for S-adenosylmethionine was 0.02 mM in the presence of 2 mM-putrescine. 6. Methylglyoxal bis(guanylhydrazone) exerted a 100% inhibition on the enzyme at a concentration of 5 μM.