title: Alkylation of an active-site cysteinyl residue during substrate-dependent inactivation of Escherichia coli S-adenosylmethionine decarboxylase.
abstract: S-Adenosylmethionine decarboxylase from Escherichia coli is a member of a small class of enzymes that uses a pyruvoyl prosthetic group. The pyruvoyl group is proposed to form a Schiff base with the substrate and then act as an electron sink facilitating decarboxylation. We have previously shown that once every 6000-7000 turnovers the enzyme undergoes an inactivation that results in a transaminated pyruvoyl group and the formation of an acrolein-like species from the methionine moiety. The acrolein then covalently alkylates the enzyme [Anton, D. L., & Kutny, R. (1987) Biochemistry 26, 6444]. After reduction of the alkylated enzyme with NaBH4, a tryptic peptide with the sequence Ala-Asp-Ile-Glu-Val-Ser-Thr-[S-(3-hydroxypropyl)Cys]-Gly-Val-Ile-Ser-Pro - Leu-Lys was isolated. This corresponds to acrolein alkylation of a cysteine residue in the second tryptic peptide from the NH2 terminal of the alpha-subunit [Anton, D. L., & Kutny, R. (1987) J. Biol. Chem. 262, 2817-2822]. The modified residue derived is from Cys-140 of the proenzyme [Tabor, C. W., & Tabor, H. (1987) J. Biol. Chem. 262, 16037-16040] and lies in the only sequence conserved between rat liver and E. coli S-adenosylmethionine decarboxylase [Pajunen et al. (1988) J. Biol. Chem. 263, 17040-17049]. We suggest that the alkylated Cys residue could have a role in the catalytic mechanism.
authors.affiliation: Central Research and Development Department, E. I. du Pont de Nemours and Company, Inc., Wilmington, Delaware 19880-0328.
authors.forename: E
authors.initials: E
authors.lastname: Diaz
authors.forename: D L
authors.initials: DL
authors.lastname: Anton
mesh_terms: D012437:Adenosylmethionine Decarboxylase / Q000037:antagonists & inhibitors*; D000478:Alkylation; D000595:Amino Acid Sequence; D001665:Binding Sites; D002250:Carbon Radioisotopes; D003545:Cysteine; D004926:Escherichia coli / Q000201:enzymology*; D007700:Kinetics; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000302:isolation & purification; D012436:S-Adenosylmethionine / Q000378:metabolism / Q000494:pharmacology*; D012545:Schiff Bases; D016339:Spectrometry, Mass, Fast Atom Bombardment; D014357:Trypsin
chemical_list: D002250:Carbon Radioisotopes; D010446:Peptide Fragments; D012545:Schiff Bases; D012436:S-Adenosylmethionine; D014357:Trypsin; D012437:Adenosylmethionine Decarboxylase; D003545:Cysteine