Kinetics of glycerol uptake by the perfused rat liver Membrane transport, phosphorylation and effect on NAD redox level

Abstract

The kinetics of glycerol uptake by the perfused rat liver were determined according to a model which includes membrane transport, intracellular phosphorylation and competitive inhibition of glycerol phosphorylation by l-glycerol 3-phosphate. The membrane transport obeys first-order kinetics at concentrations below 10 mM in the affluent medium. The K m of the glycerol phosphorylation was was 10 μM and the K i of the l-glycerol 3-phosphate inhibition was 50 μM. The maximum activity ( V) was 3.70 μmoles/min per g liver wet wt. These results are similar to in vitro kinetics of the glycerol kinase, except that K i was found to be somewhat lower in the intact organ. At low glycerol concentrations, gradient exists across the liver cell membrane. The increase in the lactate to pyruvate concentration ratio during glycerol metabolism is related to the actual concentration of l-glycerol 3-phosphate, not to the rate of glycerol uptake.