title: Escherichia coli S-adenosylmethionine decarboxylase. Subunit structure, reductive amination, and NH2-terminal sequences.
abstract: S-Adenosylmethionine decarboxylase is one of a small group of enzymes that use a pyruvoyl residue as a cofactor. Histidine decarboxylase from Lactobacillus 30a, the best studied pyruvoyl-containing enzyme, has an (alpha beta)6 subunit structure with the pyruvoyl moiety linked through an amide bond to the NH2-terminal of the larger alpha subunit (Recsei, P. A., Huynh, Q. K., and Snell, E. E. (1983) Proc. Natl. Acad. Sci. U. S. A. 80, 973-977). To examine potential structural analogies between the two enzymes, we have isolated and partially characterized S-adenosylmethionine decarboxylase. The purified enzyme comprises equimolar amounts of two subunits of Mr = 14,000 and 19,000 (by sodium dodecyl sulfate-polyacrylamide gel electrophoresis) and has a native molecular weight of 136,000 (by gel filtration). Approximately 4 mol of [methyl-3H] adenosylmethionine are incorporated per mol of enzyme (Mr = 136,000) when the enzyme is inactivated with this substrate and NaCNBH3. These data suggest an (alpha beta)4 structure with 1 pyruvoyl residue for each alpha beta pair. The two subunits have been separated by reversed-phase high performance liquid chromatography after reduction and carboxymethylation. The smaller subunit (beta) has a free amino terminus. The amino terminus of the larger subunit (alpha) appears to be blocked by a pyruvoyl group; this subunit can be sequenced only after this group is converted to an alanyl residue by reduction with sodium cyanoborohydride in the presence of ammonium acetate. This work suggests that S-adenosylmethionine decarboxylase is structurally much more similar to histidine decarboxylase than previously thought.
mesh_terms: D012437:Adenosylmethionine Decarboxylase / Q000032:analysis* / Q000378:metabolism; D000588:Amines / Q000378:metabolism; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D002262:Carboxy-Lyases / Q000032:analysis*; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000201:enzymology*; D006640:Histidine Decarboxylase / Q000032:analysis; D046911:Macromolecular Substances; D008970:Molecular Weight
chemical_list: D000588:Amines; D000596:Amino Acids; D046911:Macromolecular Substances; D002262:Carboxy-Lyases; D006640:Histidine Decarboxylase; D012437:Adenosylmethionine Decarboxylase