title: cis-dichlorodiammineplatinum (II) as a selective modifier of the oxidation-sensitive reactive-center methionine in alpha 1-antitrypsin.
abstract: Methionine 358 in the plasma protein alpha 1-antitrypsin (alpha 1AT) is an oxidation-sensitive reactive-center residue critical for proteinase-inhibitory activity. Reaction of alpha 1AT with 20 microM to 1.67 mM cis-dichlorodiammineplatinum (II) (cis-DDP) or trans-DDP afforded concentration-dependent loss of trypsin-inhibitory activity. This effect, studied by gel electrophoresis and activity assays, is essentially independent of pH over the range 4.9-8.6. Binding assays showed covalent incorporation of 1 mol of cis-DDP into each mol of alpha 1AT. cis-DDP protected a single methionine residue from oxidation and made alpha 1AT resistant to degradation by papain, which cleaves alpha 1AT at Met358. These findings strongly suggest that cis-DDP inactivates alpha 1AT by binding exclusively to its reactive-center methionine. alpha 1AT bound twice as much platinum when reacted with trans-DDP. Because carboxamidomethylated alpha 1AT incorporated nearly 1 mol of both cis- and trans-DDP, the trans isomer apparently binds to both the reactive-center methionine and to the single cysteine residue of alpha 1AT. Because of its greater selectivity, cis-DDP is the superior reagent for modification of the alpha 1AT reactive-center methionine.
authors.affiliation: Department of Pathology, Duke University Medical Center, Durham, North Carolina 27710.
authors.forename: S L
authors.initials: SL
authors.lastname: Gonias
authors.forename: M W
authors.initials: MW
authors.lastname: Swaim
authors.forename: M F
authors.initials: MF
authors.lastname: Massey
authors.forename: S V
authors.initials: SV
authors.lastname: Pizzo
mesh_terms: D001665:Binding Sites; D002945:Cisplatin / Q000494:pharmacology*; D007536:Isomerism; D007700:Kinetics; D008715:Methionine; D010084:Oxidation-Reduction; D000515:alpha 1-Antitrypsin / Q000378:metabolism*
chemical_list: D000515:alpha 1-Antitrypsin; C034697:transplatin; D008715:Methionine; D002945:Cisplatin