Enzymes of mercapturate pathway in cultured bovine ciliary epithelial cells

Relative enzyme activities of the mercapturate pathway were determined in bovine ciliary pigmented (PE) and nonpigmented (NPE) epithelial cells in culture. Glutathione S-transferase activity was greater in PE cells than in NPE cells. Gamma-glutamyl transpeptidase activity appeared to be exclusively associated with NPE cells; the enzyme activity was virtually absent in PE cells. The level of cystine aminopeptidase activity was about the same in NPE and PE cells. N-acetyl transferase was predominantly found in NPE cells. If a similar enzyme distribution should exist in vivo in the bicellular layer of ciliary epithelium, the present result suggests that both NPE and PE cells are involved in the detoxification of xenobiotics via the mercapturate pathway, glutathione conjugation occurring primarily in the PE cells and the reactions catalyzed by the membrane-bound enzymes gamma-glutamyl transpeptidase and N-acetyl transferase taking place mainly in the NPE cells.