title: The role of acetyl-CoA carboxylase phosphorylation in the control of mammary gland fatty acid synthesis during the starvation and re-feeding of lactating rats.
abstract: Activation of acetyl-CoA carboxylase during incubation of crude extracts of lactating rat mammary gland with Mg2+ and citrate can be blocked by NaF, suggesting that it represents a dephosphorylation of the enzyme. The greater extent of activation in extracts from 24 h-starved rats (200%) compared with fed controls (70%) implies that the decrease in acetyl-CoA carboxylase activity in response to 24 h starvation may involve increased phosphorylation of the enzyme. Acetyl-CoA carboxylase was purified from the mammary glands of lactating rats in the presence of protein phosphatase inhibitors by avidin-Sepharose chromatography. Starvation of the rats for 24 h increased the concentration of citrate giving half-maximal activation by 75%, and decreased the Vmax. of the purified enzyme by 73%. This was associated with an increase in the alkali-labile phosphate content from 3.3 +/- 0.2 to 4.5 +/- 0.4 mol/mol of enzyme subunit. Starvation of lactating rats for 6 h, or short-term insulin deficiency induced by streptozotocin injection, did not effect the kinetic parameters or the phosphate content of acetyl-CoA carboxylase purified from mammary glands. The effects of 24 h starvation on the kinetic parameters and phosphate content of the purified enzyme were completely reversed by re-feeding for only 2.5 h. This effect was blocked if the animals were injected with streptozotocin before re-feeding, suggesting that the increase in plasma insulin that occurs on re-feeding was responsible for the activation of the enzyme. The effects of re-feeding 24 h-starved rats on the kinetic parameters and phosphate content of acetyl-CoA carboxylase could be mimicked by treating enzyme purified from 24 h-starved rats with protein phosphatase-2A in vitro. Our results suggest that, in mammary glands of 24 h-starved lactating rats, insulin brings about a dephosphorylation of acetyl-CoA carboxylase in vivo, which may be at least partly responsible for the reactivation of mammary lipogenesis in response to re-feeding.
mesh_terms: D000103:Acetyl-CoA Carboxylase / Q000378:metabolism*; D000818:Animals; D005227:Fatty Acids / Q000096:biosynthesis*; D005260:Female; D005502:Food; D007700:Kinetics; D007774:Lactation / Q000378:metabolism*; D008025:Ligases / Q000378:metabolism*; D008321:Mammary Glands, Animal / Q000201:enzymology*; D010710:Phosphates / Q000378:metabolism; D010749:Phosphoprotein Phosphatases; D011247:Pregnancy; D054648:Protein Phosphatase 2; D051381:Rats; D011919:Rats, Inbred Strains; D013217:Starvation / Q000201:enzymology
chemical_list: D005227:Fatty Acids; D010710:Phosphates; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D008025:Ligases; D000103:Acetyl-CoA Carboxylase