The terminal oxidases in the respiration of the embryos and young roots of barley

Abstract

Cytochromes, cytochrome oxidase and ascorbic oxidase are present in barley embryos; polyphenol oxidase is absent. The cytochrome system carries about 80% of the respiratory transfer of electrons to atmospheric oxygen as indicated by cyanide, azide and carbon monoxide inhibitions. The carbon monoxide inhibition is reversed by light. Ascorbic oxidase, though present, plays no considerable part in the electron transfer, since there is very little inhibition by sodium diethyldithiocarbamate (dieca). The reaction mechanism in young roots is quite different. The cytochrome system and polyphenol oxidase are both absent, and the only oxidase yet identified is ascorbic oxidase. Respiration is not inhibited by carbon monoxide; but strongly, though not completely, inhibited by dieca. The evidence is taken to show that in the absence of the cytochrome system electron transfer continues through ascorbic oxidase.