The effect of biotin deficiency and dietary protein content on lipogenesis, gluconeogenesis and related enzyme activities in chick liver

Abstract

Chicks were given biotin-deficient diets containing either suboptimal (low) or supraoptimal (high) concentrations of protein from 1-day-old until they were used during their 4th wk of life. The low-protein diet predisposed chicks to develop fatty liver and kidney syndrome and the high-protein diet to develop classical biotin deficiency signs. Two other groups, as controls, received biotin-supplemented rations. Low dietary protein increased lipogenesis by isolated hepatocytes but had little effect on gluconeogensis compared to high dietary protein. Low dietary protein decreased activities of hepatic isocitrate dehydrogenase (EC 1.1.1.42), fructose-1,6-bisphosphatase (EC 3.1.3.11) and glucose-6-phosphatase (EC 3.1.3.9; GP) and increased activities of fatty acid synthase (FAS), citrate cleavage enzyme (EC 4.1.3.8; CCE) and malate dehydrogenase (decarboxylating) (EC 1.1.1.39). When biotin deficiency was superimposed, the rate of lipogenesis by isolated hepatocytes (from fed birds) was decreased. Gluconeogensis from lactate and glycerol was also depressed. Activity of GP was further decreased by biotin deficiency on the low-protein regimen and FAS nad CCE were further increased. PK [pyruvate kinase (EC 2.7.1.40)] activity was increased by biotin deficiency.