Evidence for the presence of two terminal oxidases in the trypanosomatid Crithidia oncopelti.

Increasing concentrations of cyanide inhibited the respiration of whole cells of Crithidia oncopelti in a biphasic fashion. Approximately 80% inhibition was attained with 40 microM-KCN. No further inhibition occurred until the concentration of KCN reached approximately 200 microM. Thereafter inhibition rose gradually to 100% at 1500 microM-KCN. Difference spectra revealed the presence of two CO-reacting haemoproteins. These were shown to be two different functional oxidases by photochemical action spectra obtained by using laser light. One oxidase was identified as cytochrome a + a3 whilst the other had the properties of cytochrome o. Both oxidases could be detected in cells at all stages of growth by the above methods.