Substrate Specificity of Human Glutamine Transaminase K as an Aminotransferase and as a Cysteine S-Conjugate Beta-Lyase
Biochemistry and Molecular Biology
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.
Cooper, A. J., Pinto, J. T., Krasnikov, B. F., Niatsetskaya, Z. V., Han, Q., Li, J., et al. (2008). Substrate specificity of human glutamine transaminase K as an aminotransferase and as a cysteine S-conjugate beta-lyase. Archives of Biochemistry and Biophysics, 474(1), 72-81. doi:10.1016/j.abb.2008.02.038
Originally published in Archives of Biochemistry and Biophysics. https://doi.org/10.1016/j.abb.2008.02.038