Sedimentation coefficient determinations show that, under comparable conditions, pig liver phosphofructokinase (PL-PFK) is larger than any previously studied phosphofructokinase; the molecular weight of PL-PFK at 4 °C at a protein concentration of 5 mg/mL is estimated to be greater than 10 000 000. Furthermore, the enzyme is very asymmetric as indicated by a strong concentration dependence of the sedimentation coefficient data and by a minimum intrinsic viscosity value at 20.0 °C of 30.8 cm3/g. Kinetic and reversibility tests show that the enzyme exists as a temperaturedependent, concentration-dependent equilibrium mixture of polymeric forms. Dissociation (partial) is favored by either higher temperatures or lower protein concentrations. PL-PFK sediments as a single peak (s02o,w = 104 S) at both 4 and 23 °C, at concentrations above 3 and 9 mg/mL, respectively.An mammals, control of liver phosphofructokinase (PFK)1 is necessary for coordination of utilization of glucose through glycolysis and synthesis of glucose through gluconeogenesis.In addition, these reactions must be coordinated with the overall needs for, and supplies of, carbohydrates from all sources, including amino acids, Krebs cycle metabolites, fatty acids, etc. In this respect, the mammalian liver PFKs differ from their widely studied muscle counterparts, which, for the most part, are turned on or off only in response to needs for energy through degradation of glucose. This difference in complexity of functions raises the possibility of differences in structures and control properties between mammalian muscle and liver phosphofructokinases.Although procedures have recently been published for purification of phosphofructokinases from various liver sources,

No abstract

No abstract

No abstract

No abstract