Evidence for the Presence of Two Terminal Oxidases in the Trypanosomatid Crithidia oncopelti

Summary: Increasing concentrations of cyanide inhibited the respiration of whole cells of Crithidia oncopelti in a biphasic fashion. Approximately 80% inhibition was attained with 40 μM KCN. No further inhibition occurred until the concentration of KCN reached approximately 200 μm. Thereafter inhibition rose gradually to 100% at 1500 μm-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.