Previous studies showed that livers from carnivorous birds have a higher gluconeogenic capacity and higher levels of gluconeogenic enzymes than livers from granivorous birds. In this work we compare the effects of fasting and adrenalectomy on gluconeogenesis. Fasting in the chicken elicited increased rates of incorporation of 14C from alanine into blood glucose, increased gluconeogenesis in liver slices, and increased activities of four gluconeogenic enzymes: glucose-6-phosphatase, phosphoenolpyruvate carboxykinase, alanine aminotransferase, and aspartate aminotransferase. These responses in the chicken resemble those observed in fasted rodents. In marked contrast, fasting in black vultures induced decreased rates of incorporation of alanine label into circulating glucose, decreased gluconeogenesis in liver slices, and no change in any of the four enzymes studied. This unusual response to fasting in the carnivorous bird is probably related to the high-protein-low-carbohydrate content of the diet. Fasted adrenalectomized birds (granivorous and carnivorous) had reduced rates of in vivo glucose synthesis, decreased liver gluconeogenesis, and lower activity of glucose-6-phosphatase and aspartate aminotransferase, without change in phosphoenolpyruvate carboxykinase and alanine aminotransferase activities.

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Pyruvate kinase from Mucor rouxii constitutes a family of three isoenzymes which can be separated in DEAE-cellulose columns. These have been named type I, I1 and 111. They also have different electrophoretic mobility in polyacrylamide gels. Pyruvate kinases type I, I1 and I11were partially purified by ion-exchange chromatography. Antisera were prepared against types I and 111. The antigenic behaviour of the three isoenzymes supported the hypothesis on the hybrid nature of pyruvate kinase type I1 and confirmed the identity of pyruvate kinase from yeastlike cells and type I from mycelium.The filamentous form contains the three types, none of them being constitutive and the proportion of each depends on the concentration and on the nature of the carbohydrate in the growth medium. Under gluconeogenic conditions of growth type 111 predominantes while in any condition in which aerobic glycosis is favoured type I is the dominant form. We also show the results of a detailed study of the effects of nutritional factors on the enzymatic pattern of pyruvate kinases in M . rouxii.Evidence is presented indicating that under a variety of conditions the filamentous form contains the three forms of the enzyme, which can be distinguished from each other on DEAE-cellulose columns. None of the three forms seems to be constitutive, the relative proportions of each form vary according to the growing conditions as well as to the morphology of the fungus. Kinetics of induction of pyruvate kinase I1 and I11 during aerobic germination of spores under gluconeogenic conditions, accompanied by disappearance of type I and also reappearance of types I and I1 upon addition of glucose or xylose to growing cultures devoid

Kinetic studies with [2-3H]glucose in vivo and gluconeogenic activity measurements in vivo and in vitro were performed in 70% hepatectomized rats submitted to fasting, which represents an extra burden for glucose synthesis but does not impair liver regeneration. Rates of glucose replacement, under steady-state conditions, 14 and 24 h postoperatively, did not differ in partially hepatectomized fasted rats and sham-operated controls. Phosphoenolpyruvate carboxykinase activities increased more rapidly during fasting in remnant livers than in intact livers from controls. Rates of incorporation of 14C from alanine into circulating glucose in hepatectomized rats were already maximal 14 h after surgery, whereas in controls they continued to augment. The maximal rates after partial hepatectomy could not be surpassed by performing the operation in diabetic animals. It is concluded that the relatively high blood sugar levels during fasting in hepatectomized rats do not depend on a reduced peripheral utilization of glucose, but only on a rapid increase in the gluconeogenic activity. The data suggest that hepatocytes in remnant liver can proliferate under conditions of maximal gluconeogenic and low glycolytic activities.

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