Substrate specificity of human glutamine transaminase K as an aminotransferase and as a cysteine S-conjugate beta-lyase |
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Authors: | Cooper Arthur J L Pinto John T Krasnikov Boris F Niatsetskaya Zoya V Han Qian Li Jianyong Vauzour David Spencer Jeremy P E |
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Affiliation: | a Department of Biochemistry and Molecular Biology, New York Medical College, Valhalla, NY, USA b Burke Medical Research Institute, White Plains, NY, USA c Department of Biochemistry, Virginia Tech, Blacksburg, VA, USA d Molecular Nutrition Group, School of Chemistry, Food and Pharmacy, University of Reading, Reading, UK |
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Abstract: | Rat kidney glutamine transaminase K (GTK) exhibits broad specificity both as an aminotransferase and as a cysteine S-conjugate β-lyase. The β-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 β-lyase. S-(1,1,2,2-Tetrafluoroethyl)-l-cysteine is an excellent aminotransferase and β-lyase substrate of rhGTK. Moderate aminotransferase and β-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 α-keto acids generated by transamination/l-amino acid oxidase activity of the two catechol cysteine S-conjugates are unstable. A slow rhGTK-catalyzed β-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 β-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. |
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Keywords: | Cysteine S-conjugate β-lyase 5-S- smallcaps" >l-cysteinyl- smallcaps" >l-DOPA 5-S- smallcaps" >l-cysteinyldopamine Glutamine transaminase K Se-methyl- smallcaps" >l-selenocysteine |
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