Shuttles for translocation of NADH in isolated liver cells from fed rats during oxidation of xylitol.

Translocation of xylitol-derived NADH via malate-aspartate and alpha-glycerophosphate shuttles was studied in liver cells isolated from fed rats. In bicarbonate medium amino-oxyacetate, rotenone and antimycin A, were equally efficient in depressing the xylitol removal. Incubation of cells in nonbicarbonate medium did not affect the rate of xylitol removal. In this medium amino-oxyacetate and antimycin A, but not rotenone, inhibited xylitol removal. Xylitol inhibited the lactate accumulation found when the cells were incubated without any exogenous substrates. Glucose was the main end product of xylitol oxidation. In nonbicarbonate medium ketogenesis was high, whereas in bicarbonate medium a low rate of ketone body formation was found. Xylitol had no effect on the rate of ketone body formation in either medium tested. Xylitol markedly decreased the ATP and Pi contents of the cells, but no change in the ATP/ADP x Pi ratio or the rate of oxygen consumption was found. The results suggest that NADH formed during xylitol oxidation is translocated to the mitochondria mainly through the malate-aspartate shuttle and only when this shuttle is inhibited does the alpha-glycerophosphate shuttle transfer NADH. Intramitochondrial reactions which form NADH and FADH2 are also suggested to be important regulators of the activity of the alpha-glycerophosphate shuttle.