Rapid modulation of adipocyte phosphofructokinase activity by noradrenaline and insulin

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Abstract
Alterations in phosphofructokinase properties can be reproducibly seen in tissue extracts prepared and rapidly assayed after exposure of rat adipocytes to hormones. Noradrenaline [norepinephrine, NE] ACTH or isoprenaline (isoproterenol; .beta.-adrenergic agonist) decreased the activity measured with high fructose 6-phosphate concentrations (3-6 mM), but increased activity measured with lower concentrations of this substrate (0.3-0.9 mM). NE decreased the Vmax and the concentration of fructose 6-phosphate that gave half the Vmax. Insulin opposed the actions of NE and itself increased phosphofructokinase activity. The effect of NE appeared to be exerted through a .beta.-rather than an .alpha.-type of adrenoceptor. The effects of NE to decrease phosphofructokinase activity at high fructose 6-phosphate concentrations and to increase activity at low fructose 6-phosphate concentrations could be rapidly reversed in cells by addition of the .beta.-blocker propranolol. The effect of NE seen at low fructose 6-phosphate concentrations could be abolished by homogenization of cells in buffer containing albumin or reversed by brief incubation of tissue extracts with albumin, suggesting that this effect of the hormone is due to the association of some ligand with the enzyme.