The reduction of disulphides by rat liver mitochondria.

The capacity of rat liver mitochondria to reduce 23 non-protein disulphides to their thiols has been examined. The best reduced include the three intermolecular disulphides, bis(2-aminoethyl)disulphide (cystamine, basic), bis(2-hydroxyethyl)disulphide (HED, neutral and bis(3-carboxypropyl)disulphide (CPD, acidic). Their behaviour has been compared. In each case the thiol formed is found in highest concentration in the mitochondrial matrix. The three disulphides require an NAD-reducing substrate and respond similarly to changes in the initial disulphide concentration, pH of the medium and inhibitors. The most effective of these are N-ethylmaleimide, phenylarsenoxide (shown to be a potent swelling agent), triethyltin and 1-chloro-2,4-dinitrobenzene (CDNB). The fall in GSH induced by the latter correlates with the extent of inhibition. An uncoupler (carbonylcyanide-m-chlorophenylhydrazone, CCCP) inhibits reduction of HED and CPD but not that of cystamine. After lysis of mitochondria there is no significant reduction even in the presence of NADH or NADPH. Reduction is observed in sonicates if lipoamide is added with NADH but this reaction is insensitive to CDNB and CPD is not reduced. Also neither cystamine nor HED supports pyruvate dehydrogenation. There is also reduction if GSH and glutathione reductase are added with NADPH. All three disulphides are reduced to some extent but the rates for HED and especially CPD are inadequate to account for the rates in intact mitochondria.