Regulation of Hexokinase in a Freeze Avoiding Insect: Role in the Winter Production of Glycerol

摘要

Hexokinase from larvae of the freeze-avoiding goldenrod gall Iloth, Epiblema scudderiana, was purified 20-fold using chro- Ilatography on DE52 Sephadex, phosphocellulose, and blue dex- ran. Final specific activity was 75.8 U/mg and SDS-PAGE gave l molecular weight of 94,000 for the monomer. Arrhenius plot :howed a break at 16° or 12°C in the absence vs. presence of .0% v/v glycerol, indicating a conformational change in the en- :yme at lower temperatures but suggesting a stabilizing effect If glycerol. Comparison of hexokinase kinetic properties at 22° rnd 4°C showed higher affinity for both glucose and ATP (KIn ralues were 45-50% lower), as well as for the cofactor Mg~(2+), at he lower temperature. Furthermore, product inhibition by glu- :ose-6-phosphate and ADP was reduced at 4°C. Glucose levels ise in E. scudderiana as an apparent by-product of high rates )f glycogenolysis during glycerol synthesis. The temperature- lependent properties of hexokinase would facilitate the recy- ~ling of this glucose back into the pathway of glycerol synthesis md could help to achieve the near stoichiometric conversion )f glycogen to glycerol that is seen during cold hardening. Arch. Insect Biochem.