Phosphofructokinase from Liver of the Rainbow Trout, Oncorhynchus mykiss

Phosphofructokinase (PFK) from liver of the rainbow trout Oncorhynchus mykiss was purified to homogeneity with a recovery of 35% of total activity. The purified enzyme was a homotetramer with a native molecular weight of 297,000 ± 16,000 and a subunit Mr of 76,000 ± 3000. Arrhenius plots of enzyme activity were linear over 5-27°C with an activation energy of 52.3 ± 2.1 kJ/ mol. The binding of fructose 6-phosphate was cooperative. High ATP increased the Hill coefficient and produced a marked allotropic inhibition of the enzyme activity. The affinity of the enzyme for fructose 6-phosphate was increased by the addition of the enzyme activators such as inorganic phosphate, ammonium ions, AMP, and fructose 2,6-bisphosphate; the activators also reduced the inhibitory effect of ATP. Trout liver PFK was activated by phosphoenolpyruvate at physiological concentrations but was not affected by citrate.