Determination of Metabolite Compartition in Hepatic Cells by Varying the Redox State in vivo

Abstract

In the present study, metabolite (lactate, pyruvate, glycerol 3-phos- phate, dihydroxyacetone phosphate) concentrations were measured in various redox states. The mathematical relations between metabolite concentrations in various redox states were expressed algebraically and studied. Models which provided separate lactate/pyruvate (L/P) and glycerol 3-phosphate/dihydroxyacetone phosphate (G/D) spaces correspond to the experimental results in the case of “reductants” (e.g. ethanol, acetaldehyde, dihydroxyacetone and acetate) or of “oxidizing agents” (e.g. pyruvate) of the cytosolic NAD-NADH. Crotonate injection caused an oxidation of cytosolic redox couples, but no separation of the lactate/pyruvate space from the glycerol 3-phosphate/dihydroxyacetone phosphate space may necessarily be inferred. Furthermore, the following statements could be made in both first cases: (i.e. of “reductants” and “oxidizing agents”):

(a) Redox couples in L/P space and in G/D space (together L/P-G/D system) are in equilibrium;

(b) Redox-equivalent transport from the L/P space to the G/D space is not subject to any velocity-limiting mechanism;

(c) Substrates which transports redox-equivalents into and from the L/P-G/D system reach concentrations to values, which are in a linear relation to each other in this system;

(d) It is possible that these substrates are regenerated in another system which is also in equilibrium and subject to statement c.