|
type |
Journal Article |
authors |
Cooper AJ, Pinto JT, Krasnikov BF, Niatsetskaya ZV, Han Q, Li J, Vauzour D, Spencer JP. |
title |
Substrate specificity of human glutamine transaminase K as an aminotransferase and as a cysteine S-conjugate beta-lyase |
journal |
Arch Biochem Biophys |
Activity |
2.6.1.64 |
sel |
selected |
ui |
18342615 |
year |
(2008) |
volume |
474 |
number |
1 |
pages |
72-81 |
| |
abstract |
Rat kidney glutamine transaminase K (GTK) exhibits broad specificity both as an aminotransferase and as a cysteine S-conjugate beta-lyase. The beta-lyase reaction products are pyruvate, ammonium and a sulfhydryl-containing fragment. We show here that recombinant human GTK (rhGTK) also exhibits broad specificity both as an aminotransferase and as a cysteine S-conjugate beta-lyase. S-(1,1,2,2-Tetrafluoroethyl)-l-cysteine is an excellent aminotransferase and beta-lyase substrate of rhGTK. Moderate aminotransferase and beta-lyase activities occur with the chemopreventive agent Se-methyl-l-selenocysteine. l-3-(2-Naphthyl)alanine, l-3-(1-naphthyl)alanine, 5-S-l-cysteinyldopamine and 5-S-l-cysteinyl-l-DOPA are measurable aminotransferase substrates, indicating that the active site can accommodate large aromatic amino acids. The alpha-keto acids generated by transamination/l-amino acid oxidase activity of the two catechol cysteine S-conjugates are unstable. A slow rhGTK-catalyzed beta-elimination reaction, as measured by pyruvate formation, was demonstrated with 5-S-l-cysteinyldopamine, but not with 5-S-l-cysteinyl-l-DOPA. The importance of transamination, oxidation and beta-elimination reactions involving 5-S-l-cysteinyldopamine, 5-S-l-cysteinyl-l-DOPA and Se-methyl-l-selenocysteine in human tissues and their biological relevance are discussed. |
last changed |
2009/02/16 13:12 |
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