Occurrence and properties of four forms of phosphoenolpyruvate carboxykinase in the chicken liver

Abstract

A considerable activity of PEP 4 carboxykinase was found to exist in not only the mitochondrial fraction but also the cytosol fraction of the livers of chick embryo, young chick, and adult chicken. The PEP carboxykinases in the different subcellular fractions could be distinguished by DEAE-Sephadex column chromatography. The developmental changes of the levels of PEP carboxykinase in different subcellular fractions were significantly different; especially, the level of the cytosol PEP carboxykinase in the chick embryo liver was very low in the early stage of development and increased rapidly from the 16th day of incubation, reaching a maximum at 3–4 days after hatching. Also it was found that in the livers of chick embryos and very young chicks there were in total four forms of PEP carboxykinase—two in the mitochondrial fraction and two in the cytosol fraction—which could, respectively, be separated from each other by means of DEAE-Sephadex column chromatography. In contrast, the liver of adult chickens contained usually only two forms of PEP carboxykinase—one in the mitochondrial fraction and the other in the cytosol fraction. The behaviors on DEAE-Sephadex column chromatography of the PEP carboxykinases in different subcellular fractions of the adult chicken liver were, respectively, quite the same as those of one of the two PEP carboxykinases in the corresponding subcellular fractions of the livers of chick embryos and young chicks. All forms of PEP carboxykinase showed apparently the same molecular weight of about 24,000 by gel filtration, and their isoelectric points were in the range of 4.95–5.05. Also no appreciable difference could be observed between those various forms of PEP carboxykinase with respect to the apparent K m values for oxaloacetate, GTP, PEP, and GDP. The cytosol enzymes were less stable against heat than the mitochondrial enzymes.