“…The total 02 outputs were close to theory in all cases (Table 5) It is well known that quinones formed by the action of polyphenol oxidase can bring about secondary oxidations, e.g. coenzyme I (Dixon & Zerfas, 1940), coenzyme II (Kubowitz, 1937), ascorbic acid (Robinson & Nelson, 1944), aminoacids (Happold & Raper, 1925;James, Roberts, Beevers & De Kock, 1948). Evidence has been presented that tyrosinase may act as a terminal oxidase in plant respiration, the quinone acting as a hydrogen acceptor (e.g.…”