Different gamma-glutamyl transpeptidase mRNAs are expressed in human liver and kidney

In human, the two subunits of gamma-glutamyl transpeptidase (GGT) arise from a common precursor encoded by a multigene family. Until now, a single specific coding sequence for this precursor (type I) has been identified in human placenta and liver. In the present study, we have isolated from a human kidney cDNA library, a GGT specific clone (0.8 Kb). The sequence of which (type II) i) covers the carboxy terminal part of the GGT precursor, ii) exhibits 22 point mutations and a 30 bp deletion as compared to the type I GGT sequence. The sequencing of a human genomic clone reveals that this type II GGT mRNA is encoded by a different gene than the type I GGT mRNA. Both type I and type II GGT mRNAs are expressed in human liver, while almost exclusively type II GGT mRNA is detected in human kidney.