Clearance of different multiple forms of human gamma-glutamyltransferase.

Several multiple forms of gamma-glutamyltransferase (EC 2.3.2.2) have been described in serum. Most of these are large complexes between the enzyme and circulating lipoproteins. One dominating form is complexed with high-density lipoprotein; a small, hydrophilic form is present in minor amounts. We purified the two forms by immunoaffinity chromatography, injected the purified forms into rabbits, and studied the clearance of the two forms by measuring the change in enzyme activity and in enzyme protein concentration with an enzyme-linked immunosorbent assay. The half-life of the hydrophilic enzyme was 9 h; that of the lipoprotein-enzyme complex was 20 h. This indicates that the lipoprotein-enzyme complex accumulates in serum relative to the hydrophilic enzyme, suggesting in part an explanation of the dominance of the larger form in disease.