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.
Abraham
D G
DG
Department of Biochemistry, Cornell University Medical College, New York, New York 10021, USA. dickyvabraham@merck.com
Cooper
A J
AJ
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