Effect of hydroxycobalamin on the inhibition of cytochrome c oxidase by cyanide. I - In intact mitochondria.

The effects of hydroxycobalamin on inhibition of cytochrome c oxidase by cyanida in isolated intact mitochondria were studied. No effect of hydroxycobalamin (HCo) and cyanocobalamin (CNCo) was observed on normal mitochondria. When mitochondria inhibited by cyanida were treated with HCo the respiration with ADP, the respiration after ADP and respiratory coefficient (RC) were increased. No effect was observed with CNCo. Difference spectra of the effect of HCo on the inhibition of cytochrome c oxidase by cyanida and azide in isolated intact mitochondria were recorded using a split beam spectrophotometer. The results presented herein suggest that HCo reverses the cyanide inhibition because part of cytochrome a3 is free from cyanide as a consequence of dissociation of the complex, resulting in CNCo formation. If this reaction continues to occur together with a probable by pass between cytochrome a and oxygen throught the HCo (which was not transformed in CNCo), oxygen consumption and most of the respiratory chain will be maitened in the active state.