Streptomyces L-methionine decarboxylase: purification and properties of the enzyme and stereochemical course of substrate decarboxylation.
L-Methionine decarboxylase from Streptomyces species ATCC 21020 has been purified to near homogeneity, characterized, and compared to the enzyme from the fern Dryopteris filix-mas [Stevenson, D.E., Akhtar, M., & Gani, D. (1990) Biochemistry (first paper of three in this issue)]. The enzyme catalyzes the decarboxylation of a range of alkylamino acid substrates, but the substrate specificity is different from that for the fern enzyme. In accord with the properties of the fern enzyme, the Streptomyces enzyme is also a homodimer of Mr 100,000 +/- 5000 and requires PLP for activity. At low pH where the value of Vmax for both enzymes is maximal and essentially pH independent, kcat for the Streptomyces enzyme with (2S)-methionine as substrate is slightly higher (60 s-1) than the value for the eukaryotic protein (50 s-1). The pH optimum for V/K is much higher than that for the fern enzyme although many features of the pH dependence are similar, including the shape of the curve for the pH dependence of Km. When the decarboxylations of (2S-methionine, (2S)-norleucine, and (2R)-S-ethyl-L-cysteine were conducted on a preparative scale in protium and deuterium oxide, unlabeled and deuteriated amines were formed. 1H NMR spectroscopic analysis of the stereochemistry at C-1 of the camphanamide derivatives of the products [Stevenson, D. E., Akhtar, M., & Gani, D. (1990) Biochemistry (first paper of three in this issue)] indicated that each conversion was stereospecific and occurred with retention of configuration at C-2 of the substrates.(ABSTRACT TRUNCATED AT 250 WORDS)
Stevenson
D E
DE
Department of Chemistry, University of Southampton, U.K.
Akhtar
M
M
Gani
D
D
D002262:Carboxy-Lyases / Q000737:chemistry / Q000378:metabolism*; D003653:Decarboxylation; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D013237:Stereoisomerism; D013302:Streptomyces / Q000201:enzymology*; D013379:Substrate Specificity
D002262:Carboxy-Lyases; C066836:methionine decarboxylase