HIGH-LEVEL EXPRESSION OF FUNCTIONAL HUMAN GAMMA-GLUTAMYL-TRANSPEPTIDASE USING THE BACULOVIRUS SYSTEM

The understanding of the structure and function of gamma-glutamyl tran speptidase (GGT) has been hindered by the difficulty of obtaining larg e quantities of functional enzyme. A recombinant baculovirus, encoding the human hepatoma cell (Hep G2) GGT, was easily purified using a his tochemical procedure to reveal GGT activity. Infected insect cells syn thesized a large amount of enzymatically active GGT representing up to 10% of the total cell extract protein. The GGT specific activity of t he infected cells was 13 units per mg of protein which is the highest GGT expression level reported to date, 260-times more than in Hep G2 c ells. The recombinant protein displayed an apparent molecular mass (Mr , 58,000 for the heavy subunit), immunoreactivity and catalytic featur es similar to those of the native protein. The high-level expression o f functional GGT should provide an excellent tool to further study the structure-function relationships of the protein.