Participation of Cytochromes in the Respiration of the Aroid Spadix.

Although a cyanide-resistant fraction of respiration is present in many plant and animal tissues, the mechanism of terminal oxidation in such respiration has never been completely clarified. On the basis of their study of the rapid, cyanide-resistant respiration of the Aroid spadix, James and Beevers (8) proposed that flavoproteins serve as terminal oxidases in this tissue. Their conclusion was based in part on the finding that the measured respiratory rate was strongly dependent upon the partial pressure of oxygen. In addition, they found no spectroscopic or enzymatic evidence for the presence of a cytochrome system. The rapid respiration of the Aroid spadix has been reinvestigated here. A relative insensitivity to cyanide (HCN) and carbon monoxide (CO) has been confirmed. With an adequate rate of oxygen supply, the tissue exhibits a very high affinity for oxygen. This observation led to a spectroscopic and enzymatic search for cytochrome components. The results reported here demonstrate the participation of cytochromes in the respiration of the Aroid spadix. A preliminary report of the results was given earlier (23).