Zinc deficiency-induced changes in the composition of microsomal membranes and in the enzymatic regulation of glycerolipid synthesis.

The effects of zinc deficiency and/or castration on the lipid composition of microsomal membranes of liver, small intestine and testes were studied in rats. The result showed that feeding a zinc-deficient diet to castrated rats decreased phospholipid content and consequently increased the cholesterol-to phospholipid ratio in liver microsomes. An increase in cholesterol-to phospholipid ration occurred also in small intestine and testes microsomes from rats fed the zinc-deficient diet. It is postulated, therefore, that zinc deficiency alters the lipid composition and fluidity of microsomal membranes. Zinc deficiency also affected tha activities of the enzymes involved in the formation of triglycerides and phospholipids. There was a large increase in total and specific activity of phosphatidate phosphatase and the changes in the total activity of choline phosphotransferase correlated well with the changes observed in serum or liver triglycerides and phospholipids. Stearoyl CoA desaturase, which is a control enzyme for hepatic lipogenesis, was also increased by more than 200% in zinc-deficient states, as was the diglyceride content of hepatic microsomes. These results indicate that the increased synthesis of triglycerides and phospholipids in zinc deficiency may be due to the increased availability of substrates as well as to increased activities of the enzymes involved in these processes.