Define regulation of L-PK enzymes by starvation & refeeding?
L-PK catalyzes the conversion of phosphoenolpyruvate to pyruvate and plays an important role in directing pyruvate toward glucose synthesis in starved animals or towards oxidation of and incorporation into long-chain fatty acids in fed animals. The level of L-PK decreases greatly in starved rats and is increased when starved rats are refed, particularly if the diet contains a high level of carbohydrate. In diabetic animals, L-PK concentration is very low; treatment with insulin restores normal levels. Feeding a diet high with insulin restores normal levels. Feeding a diet high in fructose, but not glucose, partly restores the normal level of L-PK in a diabetic rat. These changes in concentration of L-PK are due to changes in the synthesis rate of the protein. Thyroid hormone also stimulates accumulation of L-PK protein in thyroidectomized rats.
The level of L-PK and WA is increased in rats treated with insulin and decreased in diabetic animals or animals treated with glucagon s or cyclic adenosine monophosphate (CAMP). Fructose and certain other simple sugars cause an increased accumulation of L-PK and its mRNA, even in diabetic animals. Regulation of rate of synthesis of L-PK mRNA is not exclusively transcriptional, and different hormones may regulate expression of this gene by regulating different reactions in the gene expression pathway.