Molecular cloning and expression of a cDNA for human kidney cysteine conjugate β‐lyase

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Abstract
Kidney cysteine conjugate β-lyase (glutamine transaminase K, kyneurenine aminotransferase, EC 2.6.1.64) metabolises the cysteine conjugates of certain halogenated alkenes and alkanes to form reactive metabolites which can produce nephrotoxicicity and neurotoxicicity in experimental animals and man. Using a combination of hybridisation screening and PCR techniques we have isolated a full-length cDNA for human kidney cysteine conjugate β-lyase. Comparison of the deduced amino acid sequence with that of the rat enzyme indicated an 82% overall similarity, with 90% similarity around the pyridoxal phosphate binding site, many of the changes being conservative in nature. Expression of the cDNA in Cos-1 cells resulted in the production of a cytosolic enzyme which showed both cysteine conjugate β-lyase and glutamine transaminase K activity. Preliminary mapping of the gene for human cysteine conjugate β-lyase by PCR analysis of genomic DNA from human-rodent hybrid cells indicated that it is located on human chromosome 9.