Cloning and expression of a rat kidney cytosolic glutamine transaminase K that has strong sequence homology to kynurenine pyruvate aminotransferase.
An alpha-keto acid-dependent cysteine S-conjugate beta-lyase of rat kidney was identified as cytosolic glutamine transaminase K by Stevens et al. (J. Biol. Chem. 261, 15529-15537, 1986). Subsequently, a rat kidney protein with both glutamine transaminase K- and cysteine S-conjugate beta-lyase activities was cloned and sequenced by Perry et al. (Mol. Pharmacol. 43, 660-665, 1993). This protein was later shown to be identical with kynurenine pyruvate aminotransferase (Mosca et al., FEBS Lett. 353, 21-24, 1994). Thus, kynurenine pyruvate aminotransferase possesses both glutamine transaminase K- and cysteine S-conjugate beta-lyase-type activities. We have also cloned a cytosolic glutamine transaminase K from a rat kidney cDNA library and expressed the full-length clone in COS1 cells. The transfected cells exhibit marked increases in activities of both glutamine transaminase K and cysteine S-conjugate beta-lyase. The enzyme cloned in the present work is a homodimer. Each subunit has a molecular mass of 45.8 kDa and contains 426 amino acid residues. The sequence of cytosolic glutamine transaminase K obtained in the present work has strong similarities to other aminotransferases, including >90% identity with kynurenine pyruvate aminotransferase. Our preparation of purified rat kidney cytosolic glutamine transaminase K possesses some kynurenine pyruvate aminotransferase activity. Thus, rat kidney cytosol possesses at least two distinct enzymes that catalyze glutamine transaminase K/cysteine S-conjugate beta-lyase/kynurenine pyruvate aminotransferase reactions. The present work underscores the difficulties associated with characterizing aminotransferases with overlapping specificities.
Department of Biochemistry, Cornell University Medical College, New York, New York 10021, USA. dickyvabraham@merck.com
D G
DG
Abraham
A J
AJ
Cooper
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D019556:COS Cells; D003001:Cloning, Molecular; D003600:Cytosol / Q000201:enzymology; D015870:Gene Expression; D007668:Kidney / Q000201:enzymology; D008190:Lyases / Q000235:genetics*; D008969:Molecular Sequence Data; D011732:Pyridoxal Phosphate / Q000378:metabolism; D051381:Rats; D012689:Sequence Homology, Nucleic Acid; D014018:Tissue Distribution; D000637:Transaminases / Q000235:genetics*; D014162:Transfection
D011732:Pyridoxal Phosphate; D000637:Transaminases; C427605:glutamine - phenylpyruvate transaminase; C021481:kynurenine-oxoglutarate transaminase; D008190:Lyases