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The properties of proteolytically non-modified phosphofructokinase from baker's yeast were investigated by means of hydrodynamic, electrophoretic, and chemical methods. The sedimentation coefficient shows a linear dependence on the protein concentration down to 0.01 mg/ml. The sedimentation coefficient has been determined to be s20,w = 20.81 S. At concentrations of the enzyme at less than 0.01 mg/ml a significant decrease of this value was found.The partial specific volume of the enzyme as determined by three different methods at 20 "C is u2 = 0.742 ml/g.From equilibrium sedimentation a molecular weight of 835000 32000 was calculated for the native enzyme.Amino acid analysis of the enzyme was performed and the number of half-cystine residues determined as 11/1OOOOOg is in good agreement with the number of titratable -SH groups after denaturation of the enzyme.The subunit molecular weight was determined by applying equilibrium sedimentation in the presence of sodium dodecylsulphate. Taking into account that 0.37 g of dodecylsulphate is bound per g of the enzyme protein as found by equilibrium dialysis, a subunit molecular weight of 104000 could bc calculated. This value is about 15% smaller than that obtained by gel electrophoresis in the presence of sodium dodecylsulphate.Evidently, yeast phosphofructokinase seems to be octameric. Limited proteolysis in the presence of proteinase B from yeast was investigated by following the alterations of the sedimentation coefficient, the molecular weight, and the subunit pattern of the enzyme. During partial proteolytic degradation the molecular weight of the native enzyme decreases by about 230000. This diminution is in accordance with the difference in the molecular weight per subunit if an octameric composition is considered.

Just before birth, changes occur in the metabolic capacities of rat liver so that the animal can adapt to changes in the substrate supply. In utero, glucose is the main energy-generating fuel and the liver metabolism is directed towards glucose degradation. The activities of the rate-limiting enzymes of glycolysis, hexokinase and phosphofructokinase, are high. In preparation for post-natal life, when the continuous glucose supply from the mother is interrupted, very large amounts of glycogen are stored in the late fetal liver. With the intake of the fat-rich and carbohydrate-poor milk diet, the animal develops the ability to synthesize glucose de novo from non-carbohydrate precursors. During suckling, metabolic energy is derived mainly from the beta-oxidation of fatty acids, which in turn is an essential prerequisite for the high rate of gluconeogenesis, by yielding acetyl-CoA for the activation of pyruvate carboxylase and by generating a high NADH/NAD ratio for the shift of the glyceraldehyde 3-phosphate dehydrogenase reaction in the direction of glucose formation.--The developmental adaptation of metabolism and the process of enzymatic differentiation are closely connected with the maturation of the endocrine system and the changes in the concentration of circulating hormones. The neonatal regulation of phosphoenolpyruvate carboxykinase and of tyrosine aminotransferase by variations in the hormonal milieu around birth, and also the interaction of hormonal and nutritional factors in the induction of serine dehydratase and glucokinase at the end of the suckling period, will be discussed in detail.

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