Changes in the properties of cytosolic acetyl-CoA carboxylase studied in cold-clamped liver samples from fed, starved and starved-refed rats.
We have used the cold-clamping technique to study the changes in acetyl-CoA carboxylase activity that occur in the cytosolic and mitochondrial fractions of the liver of fed, starved and starved-refed rats. No evidence was found for a role of the mitochondrial enzyme as a pool from which cytosolic carboxylase could be replenished upon refeeding of starved rats. Starvation for 24 h or 48 h induced changes in the expressed (assayed at 20 mM-citrate), total (citrate- and phosphatase-treated) and citrate-independent activities of cytosolic carboxylase, as well as in its Ka for citrate. The expressed/total activity ratio was low even in the fed state and was depressed further by starvation. The effects of refeeding occurred in two phases: an acute phase (approx. 1 h) in which the starvation-induced changes in Ka and expressed/total activity ratio were rapidly reversed, and a prolonged slow phase in which the two parameters attained values that were lower and higher, respectively, than those in the normal fed state. Refeeding also resulted in a gradual increase in citrate-independent activity of acetyl-CoA carboxylase. An additional marked increase in this activity occurred only in 48 h-starved-refed rats between 24 h and 48 h of refeeding. These findings are discussed in terms of the observed time courses of changes in lipogenic rates that occur in vivo in starved-refed rats and of the possible molecular mechanisms involved.
Moir
A M
AM
Hannah Research Institute, Ayr, Scotland, U.K.
Zammit
V A
VA
D000103:Acetyl-CoA Carboxylase / Q000378:metabolism*; D000818:Animals; D003080:Cold Temperature; D003600:Cytosol / Q000201:enzymology; D004435:Eating; D005215:Fasting; D005260:Female; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008862:Microsomes, Liver / Q000201:enzymology; D008930:Mitochondria, Liver / Q000201:enzymology; D008954:Models, Biological; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values
D000103:Acetyl-CoA Carboxylase