Regulation of phosphofructokinase and the control of cryoprotectant synthesis in a freeze-avoiding insect

Abstract

Phosphofructokinase (PFK) from larvae of the freeze-avoiding gall moth Epiblema scudderiana was purified 711-fold using ATP-agarose affinity chromatography to a final specific activity of 23 U/mg protein. The native molecular mass of the enzyme was 420 000 ± 20 000 Da. The enzyme showed an optimum pH of 8.13 ± 0.21 at22 °Cand 8.19 ± 0.11 at5 °C. Arrhenius plots of PFK activity showed a sharp break at 9 °C. S0.5 values for fructose 6-phosphate showed positive thermal modification, decreasing with decreasing assay temperature; the opposite was true for ATP-Mg2+. PFK was activated by fructose 2,6-bisphosphate, AMP, and inorganic phosphate; activator effects were temperature-dependent. The enzyme was inhibited by ATP-Mg2+, citrate-Mg2+, and phosphoenolpyruvate. The positive effects of low temperature on enzyme kinetic properties would promote PFK activity to channel glycolytic carbon flow into the production of glycerol during cold-stimulated cryoprotectant synthesis.