THE INFLUENCE OF DIETARY-PROTEIN ON THE KINETICS OF NADPH PRODUCTION SYSTEMS IN VARIOUS TISSUES OF RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

The effects of a decrease in dietary protein level on the kinetic beha viour of the four NADPH production systems [glucose 6-phosphate dehydr ogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), malic enzym e (ME), and NADP-isocitrate dehydrogenase (NADP-IDH)] were investigate d in four different trout tissues. Typical hyperbolic saturation curve s were always obtained for the activity of these enzymes. A low-protei n diet caused a significant decrease in the maximum velocity values (V (max)) of all the hepatic enzyme systems studied. The decrease in hexo se monophosphate dehydrogenases (G6PDH and 6PGDH) was about 35 and 50% , respectively, whereas for ME and NADP-IDH it was about 35 and 25%. N o significant changes were found in the Michaelis constant. These kine tic characteristics are compatible with an increase in the catalytic e fficiency of these enzymes without there being any changes in their ac tivity ratio values. The kinetic parameters for these enzymes in the k idney, spleen, and gill tissue did not undergo any significant change.