Journal of Comparative Physiology B

, Volume 159, Issue 4, pp 461–472

Metabolic correlates to glycerol biosynthesis in a freeze-avoiding insect,Epiblema scudderiana

  • Thomas A. Churchill
  • Kenneth B. Storey
Article

DOI: 10.1007/BF00692418

Cite this article as:
Churchill, T.A. & Storey, K.B. J Comp Physiol B (1989) 159: 461. doi:10.1007/BF00692418

Summary

The course of glycerol biosynthesis, initiated by exposure to −4°C, was monitored in larvae of the goldenrod gall moth,Epiblema scudderiana, and accompanying changes in the levels of intermediates of glycolysis, adenylates, glycogen, glucose, fructose-2,6-bisphosphate, and fermentative end products were characterized. Production of cryoprotectant was initiated within 6 h after a switch from +16° to −4°C, with halfmaximal levels reached in 30 h and maximal content, 450–500 μmol/g wet weight, achieved after 4 days. Changes in the levels of intermediates of the synthetic pathway within 2 h at −4°C indicated that the regulatory sites involved glycogen phosphorylase, phosphofructokinase, and glycerol-3-phosphatase. A rapid increase in fructose-2,6-bisphosphate, an activator of phosphofructokinase and inhibitor of fructose-1,6-bisphosphatase, appeared to have a role in maintaining flux in the direction of glycerol biosynthesis. Analysis of metabolite changes as glycerol production slowed suggested that the inhibitory restriction of the regulatory enzymes was slightly out of phase. Inhibition at the glycerol-3-phosphatase locus apparently occurred first and resulted in a build-up of glycolytic intermediates and an overflow accumulation of glucose. Glucose inhibition of phosphorylase, stimulating the conversion of the activea to the inactiveb forms, appears to be the mechanism that shuts off phosphorylase function, counteracting the effects of low temperature that are the basis of the initial enzyme activation. Equivalent experiments carried out under a nitrogen gas atmosphere suggested that the metabolic make-up of the larvae in autumn is one that obligately routes carbohydrate flux through the hexose monophosphate shunt. The consequence of this is that fermentative ATP production during anoxia is linked to the accumulation of large amounts of glycerol as the only means of maintaining redox balance.

Key words

Cryoprotectant synthesis Epiblema scudderiana Cold hardiness Regulation of glycolysis Fructose-2,6-biphosphate 

Abbreviations

G6P

glucose-6-phosphate

F6P

fructose-6-phosphate

F1, 6P

fructose-1,6-bisphosphate

F2,6P2

fructose-2,6-bisphosphate

G3P

grycerol-3-phosphate

DHAP

dinydroxyacetonephosphate

GAP

glyceraldehyde-3-phosphate

PEP

phosphoenolpyruvate

PFK

phosphofructokinase

FBPase

fructose-1,6-bisphosphatase

PK

pyruvate kinase

Copyright information

© Springer-Verlag 1989

Authors and Affiliations

  • Thomas A. Churchill
    • 1
  • Kenneth B. Storey
    • 1
  1. 1.Institute of Biochemistry and Department of BiologyCarleton UniversityOttawaCanada