A human hepatoma cell line expresses a single-chain form of γ-glutamyl transpeptidase
Mammalian gamma-glutamyl transpeptidases characterized thus far have been shown to be heterodimeric glycoproteins. The two subunits are derived from a single-chain propeptide which, in the rat kidney, exhibits low transpeptidase activity (less than 2% of the dimeric enzyme). A human hepatoma-derived cell line, Hep G2, expresses relatively high transpeptidase activity. The enzyme is primarily localized on the cell surface and exhibits catalytic properties similar to the dimeric human kidney and lymphoid cell transpeptidase. Significantly, the Hep G2 enzyme, unlike the enzyme from other human tissues, is a single-chain species, Mr = 120,000.