On the mechanism by which noradrenaline increases the activity of phosphofructokinase in isolated rat adipocytes.

We confirmed that, as reported by Sooranna & Saggerson [(1982) Biochem. J. 202, 753-758], the affinity of 6-phosphofructo-1-kinase (PFK) for fructose 6-phosphate in an adipocyte extract was increased after incubation of the cells in the presence of noradrenaline. The participation of fructose 2,6-bisphosphate in this kinetic modification could be excluded, because the noradrenaline effect persisted after extensive gel filtration of the extracts and also because the treatment did not cause any change in the concentration of fructose 2,6-bisphosphate in the adipocytes. Oleic acid was found to be another potent positive effector of PFK in an adipocyte extract, with a Ka of 10 microM. Its effect was synergistic with that of fructose 2,6-bisphosphate and AMP, and was counteracted by serum albumin. Palmitic acid had a similar effect. We conclude that the large increase in fatty acid concentration caused by noradrenaline treatment is an explanation for the activation of phosphofructokinase at low fructose 6-phosphate concentrations in an adipocyte extract.