The mechanism responsible for the changes in serum and liver γ-glutamyl transpeptidase (γ-GT) activity was studied in a model of experimental hexachlorobenzene porphyria in rabbits. Porphyria followed the administration of hexachlorobenzene in doses of 280 μmol • kg^-1 body weight, which were given daily through a gastric tube over a 20-day period. Serum γ-GT activity and the activities of the lysosomal enzymes β-N-acetylglucosaminidase and α-mannosidase were increased, whereas L-aspartate: 2-oxoglutarate aminotransferase and L-alanine: 2-oxoglutarate aminotransferase remained unaltered. There was a considerable increase in liver microsomal protein, γ-GT, cytochrome P-450, anilinehydroxylase,aminopyrine-demethylase and δ-aminolevulinic acid synthase. In the liverγ-GT was detected in the microsomes as well as in the cytoplasm where enzymatic activity was higher. The high correlation coefficient between liver γ-GT, cytochrome P-450 and δ-aminolevulinic acid synthase witnesses a hexachlorobenzene-induced γ-GT formation in the liver. A statistically significant correlation between serum and liver γ-GT activity was also found. These data strongly suggest that the increase in serum γ-GT activity may result from the induction of the enzyme in the liver.

Keywords:
γ-Glutamyl transpeptidase, Experimental porphyria, Hexachlorobenzene porphyria, Enzyme mechanism, Enzyme induction, Microsomal enzymes, Lysosomal enzymes
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1976
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