Vol. 172, No. 1, 1990 October 15, 1990 BIOCHEMICAL AND BIOPHYSICALRESEARCH COMMUNICATIONS Pages 328-334 REGULATION OF MUSCLE PHOSPHOFRUCTOKINASE BY PHYSIOLOGICAL CONCENTRATIONS OF BISPHOSPHORYLATED HEXOSES: EFFECT OF ALKALINIZATION Vicente Andr6s, Jos6 Carreras and Roser Cuss6* Unitat de BioqMmica, Facultat de Medicina, Universitat de Barcelona Zona Universitaria de Pedralbes, 08028-Barcelona, SPAIN Received June 29, 1990 SUMMARY: To clarify the role of glucose-l,6-P2, fructose-2,6-P2 and fructose-l,6-P2 in the control of the glycolytic flux during muscle contraction, we have determined the activity of muscle phosphofructokinase in the presence of physiological concentrations of these bisphosphorylated hexoses and other allosteric effectors, and at increasing pH values. In the presence of fructose- 2,6-P2, both glucose-l,6-P2 and fructose-l,6-P2 can additionally activate the enzyme and partially counteract citrate inhibition. Activation of phosphofructokinase produced by alkalinization increases in the presence of the bisphosphorylated hexoses. It is suggested that the hexose bisphosphates could play a significant role in the initial burst of the glycolytic flux during muscle contraction, when an alkaline pH shift is produced. ~ 199o Aoaa .......... ,~,,~. It is accepted that activation of phosphofructokinase (PFK, EC 2.7.1.11), the key regulatory enzyme of the glycolytic pathway, is involved in the enhancement of the glycolytic flux that takes place during muscle contraction, but the mechanism of this activation remains not fully understood. Among the allosteric effectors that modulate PFK activity (1,2), two sugar bisphosphates, Fru-2,6-P2 and Glu-I,6-P2, have been found in addition to the product Fru-l,6-P2. Fm-2,6-P2 could be implicated in the effects produced by insulin and adrenaline on skeletal muscle (3), but its role in the stimulation of glycolysis during mammalian muscle contraction is unclear (3-6). No relationship has been found between muscle Fru-2,6-P2 content and lactate accumulation during electrical stimulation of rat gastrocnemius muscle (4,6). * To whom correspondence should be addressed. Abbreviations used: Fru-6-P, fructose-6-phosphate; Fru-l,6-P2, fructose-l,6- P2; Fru-2,6-P2, fructose-2,6-P2; Glu-I,6-P2, glucose-l,6-P2, Glu-6-P, glucose- 6-phosphate: PFK, phosphofructokinase. 0006-291X/90 $1.50 Copyright © 1990 by Academic Press, bzc. All rights of reproduction in any j'brm reserved. 328