Mapping of human gamma-glutamyl transpeptidase genes on chromosome 22 and other human autosomes.

gamma-Glutamyl transpeptidase (GGT; EC 2.3.2.2) is a membrane-associated enzyme that plays a role in the metabolism of glutathione and in the transpeptidation of amino acids; changes in GGT activity may reflect preneoplastic or toxic conditions in the liver or kidney. In contrast to the rat, in which GGT is represented by a single gene, at least four GGT genomic sequences have been identified in man and two of these have been localized to two distinct regions of chromosome 22. To characterize this gene/pseudogene family further, we have used somatic cell hybrids to map GGT by hybridization with probes from a human kidney GGT cDNA clone and by amplification of 3' GGT sequence by PCR. We clearly map three GGT loci to chromosome 22: two loci between the centromere and the breakpoint cluster region (BCR) gene and one locus telomeric to the BCR gene. In addition, we have been able to identify GGT-related sequences on chromosomes 18, 19, and 20.