Biochemical changes in fatty liver induced by choline or threonine deficiency. Part II. Various hepatic enzymic activities during the development of fatty livers in rats

The activities of various hepatic enzymes were determined in choline-deficient rats over an 8-day experimental period and in rats fed a low-protein diet primarily deficient in threonine over a 30-day experimental period. Supernatant fractions (10,000g) prepared from rat liver homogenates were assayed for glucose-6-phosphate (+6-phosphogluconate) dehydrogenase, 6-phosphogluconate dehydrogenase, isocitrate dehydrogenase, α-glycerophosphate dehydrogenase, malic dehydrogenase, and glucose-6-phosphatase. Mitochondria isolated from rat liver homogenates were assayed for the electron transport system which catalyzes the DPN-mediated oxidation of TPNH by cytochrome c, isocitrate dehydrogenase, and α-glycerophosphate dehydrogenase. Of the enzymes assayed in the supernatant fractions (10,000g) of rat liver homogenates, only the dehydrogenases of the pentose phosphate pathway were significantly altered. A general increase in the specific activities of these enzymes occurred in all groups of rats irrespective of diet. It was concluded that the alteration in activity of these dehydrogenases may be indirectly related to the development of fatty liver by providing a source of available TPNH which could be utilized in the reductive reactions accompanying fat synthesis. Of the mitochondrial enzymes studied, only the electron transport system which catalyzes the DPN-mediated oxidation of TPNH was significantly decreased in fatty livers. The data did not permit assigning a direct cause or effect relationship between the lowered specific activity of this electron transport system and increased hepatic fat deposition; however, the correlation of lowered activity for this electron transport pathway and increased hepatic fat content was consistent.