Citrate-cleavage enzyme, ‘malic’ enzyme and certain dehydrogenases in embryonic and growing chicks

Abstract

The activities of several enzymes possibly implicated in lipogenesis were measured in the soluble fraction of homogenates of liver and adipose tissue of embryonic and growing chicks. The activities of adipose-tissue enzymes showed little or no change. The activities of hepatic hexose monophosphate-shunt dehydrogenases, malate dehydrogenase, 3-phosphoglyceraldehyde dehydrogenase and NAD-linked alpha-glycerophosphate dehydrogenase also showed little or no change. Isocitrate dehydrogenase activity in liver rose to a peak on the day of hatching and fell to half the peak value during the next 12 days, where it remained to 26 days after hatching. The activities of ;malic' enzyme and citrate-cleavage enzyme showed very low stable values in embryonic liver and remarkable rises during the early part of the post-hatching period. An 85-fold increase in the activity of ;malic' enzyme activity was completed in 7 days and a 15-fold increase in that of citrate-cleavage enzyme in 5 days. The activities then attained were maintained up to 26 days after hatching. 2. The increases in the activities of hepatic citrate-cleavage enzyme and ;malic' enzyme occurred simultaneously with a marked increase in lipogenesis, suggesting a relationship of these enzymes to lipogenesis in chick liver. By contrast, activity of the hexose monophosphate-shunt dehydrogenases does not appear to be thus associated.

Fatty Liver and Kidney Syndrome in Chicks II. Biochemical Role of Biotin

“…1971) which also metabolize glucose as a source of carbon for fatty acid synthesis, have also reported that isocitrate dehydrogenase (NADP+) is not an adaptive enzyme. Therefore isocitrate dehydrogenase (NADP+) does not appear to be an important supply of NADPH for lipogenesis in the chick, as also reported by Goodridge (1968). Malate dehydrogenase (decarboxylating) (NADP+) activities (Tables I and 2), however, are significantly higher in livers from chicks afflicted with FLKS, which implies that malate dehydrogenase (decarboxylating) (NADP+) may serve an important role in the production of reducing equivalents for fatty acid synthesis in the chicken liver, as suggested by O'Hea and Leveille (1968).…”

Regulation of the Action of Steroid/Thyroid Hormone Receptors by Medium-chain Fatty Acids

“…In the livers of well fed birds, much of the NADPH generated by this reaction is used for de novo fatty acid synthesis. Malic enzyme activity, like that of other lipogenic enzymes, is regulated by nutritional state (1,2). When starved chickens are fed or fed chickens are starved, malic enzyme activity, malic enzyme mass, malic enzyme mRNA abundance, and transcription of the malic enzyme gene increase or decrease by similar relative amounts and with time courses consistent with transcription being the primary regulated process (3,4).…”

The Homeodomain Proteins PBX and MEIS1 Are Accessory Factors That Enhance Thyroid Hormone Regulation of the Malic Enzyme Gene in Hepatocytes

“…This reaction is the primary source of reducing equivalents for de novo synthesis of long chain fatty acids in avian liver (1). Regulation of malic enzyme activity is typical of that of other lipogenic enzymes.…”

“…Nutritional regulation of malic enzyme activity is quantitatively mimicked in primary cultures of chick embryo hepatocytes by manipulating the concentrations of hormones and metabolic fuels in the culture medium. Insulin, glucose, and 3,5,3Ј-triiodothyronine (T3), 1 humoral factors that are elevated during consumption of a high carbohydrate, low fat diet, increase malic enzyme activity in chick embryo hepatocytes (3,4). T3 alone stimulates malic enzyme activity; insulin and glucose amplify the action of T3 but have little effect when added by themselves.…”