Control of the fructose 6-phosphate/fructose 2,6-bisphosphate cycle by sn-glycerol 3-phosphate.

The kinetics of PFK-2 and FBPase-2 from rat liver were investigated with respect to the substrates and the effector sn-glycerol 3-phosphate. PFK-2 exhibits a hyperbolic response with respect to its substrates Fru 6-P and ATP. The inhibition of the activity of PFK-2 by sn-glycerol 3-phosphate could be described by assuming competition with Fru 6-P at the catalytic site. sn-Glycerol 3-phosphate activates the FBPase-2 and is capable of reversing partially the inhibition of the enzyme by Fru 6-P. The dynamics of the PFK-2/FBPase-2 cycle has been investigated in an enzyme system composed of PFK-2/FBPase-2, creatine kinase and creatine phosphate. sn-Glycerol 3-phosphate was found to decrease the quasi-stationary concentration of Fru 2,6-P2. The control of the PFK-2/FBPase-2 cycle by sn-glycerol 3-phosphate turned out most efficient at high concentrations of both sn-glycerol 3-phosphate and Fru 6-P. In addition, sn-glycerol 3-phosphate was found to increase the concentration control coefficient of Fru 2,6-P2 with respect to Fru 6-P.