REGULATION OF PHOSPHOFRUCTOKINASE AND THE CONTROL OF CRYOPROTECTANT SYNTHESIS IN A FREEZE-AVOIDING INSECT

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 n ative molecular mass of the enzyme was 420 000 +/- 20 000 Da. The enzy me showed an optimum pH of 8.13 +/- 0.21 at 22-degrees-C and 8.19 +/- 0.11 at 5-degrees-C. Arrhenius plots of PFK activity showed a sharp br eak at 9-degrees-C. S0.5 values for fructose 6-phosphate showed positi ve 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 te mperature-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 glyco lytic carbon flow into the production of glycerol during cold-stimulat ed cryoprotectant synthesis.