Vitamin E deficiency in the rat. IV. Alteration in mitochondrial membrane and its relation to respiratory decline

The respiratory control and rate of oxidation of exogenous NADH in vitro by liver mitochondria from vitamin E deficient rats were studied as a means of providing information concerning possible mitochondrial membrane alterations due to the deficiency.When mitochondria were aged at different temperatures for various periods of time, half-maximal inhibition of respiratory control occurred at lower temperatures and shorter aging periods in deficient mitochondria than in normal ones. Also, respiratory control was lost more rapidly in deficient mitochondria than in normal ones in the presence of either digitonin or low (hypotonic) concentrations of mannitol.Microsomes, both freshly prepared and boiled, dramatically lowered respiratory control and the effect was greater in the deficient mitochondria. Bovine serum albumin overcame the suppressed respiratory control, and exogenously added fatty acids mimiced the action of the microsomes.NADH oxidation by normal mitochondria proceeded slowly in isotonic media, while mitochondria of vitamin E deficient rats oxidized NADH much more rapidly. When mitochondria were subjected to ultrasonic disruption or incubated in hypotonic media, the rates of NADH oxidation by both types of mitochondria were similar.Respiratory decline associated with oxidation of β-hydroxybutyrate by the deficient mitochondria was decreased by including in the medium either a high concentration of NAD⁺, 0.5 mm oxalacetate, or 2 mm aspartate plus 1 mm α-ketoglutarate. This observation, plus the finding of similar activities of malate dehydrogenase and glutamic-oxalacetic transminase in normal and deficient livers, suggests that the action of each was due to an elevation of the mitochondrial NAD⁺/NADH ratio via a malate shuttle and cytoplasmic and mitochondrial glutamic-oxalacetate transaminase. It is postulated that the marked mitochondrial respiratory decline in the deficient rats is attributed to a limiting availability of NAD⁺ and a low ratio of NAD⁺ to NADH.