Putrescine-insensitive S-adenosyl-L-methionine decarboxylase from Tetrahymena pyriformis.

Extracts of Tetrahymena pyriformis contain a soluble S-adenosyl-L-methionine decarboxylase which, in contrast to the enzyme from most eukaryotic organisms, is not stimulated by putrescine or spermidine. The protozoan adenosylmethionine decarboxylase, unlike the putrescine-insensitive enzyme form Escherichia coli, did not require any metal ions for catalytic activity either. Adenosylmethionine decarboxylase from Tetrahymena resembled the prokaryotic enzyme as far the inhibition by methylglyoxal bis(guanylhydrazone) was concerned, but behaved more like putrescine-activated enzyme in regard to the inhibition by 4-bromo-3-hydroxy benzyl-oxyamine. Adesylmethionine decarboxylase from rat liver, baker's yeast, E. coli and Tetrahymena were strongly inhibited by S-methyladenosylhomocysteamine (decarboxylated adenosylmethionine), the product of the reaction. The function of adenosylmethionine decarboxylase from Tetrahymena like that of the enzymes from other organisms appears to be closely connected to the synthesis of spermidine.