The oxidation of carotenoids by mitochondria from sugar beet leaves—III : Crocin oxidation by a peroxidase system

Abstract

The crocin-destroying system retained in the residue following treatment of mitochondrial preparations from sugar beet leaves with Triton-X-100 does not fall within the lipid-requiring category of catalysts which oxidize carotenoids. The system is similar to indole-acetic acid oxidase of plant tissues with respect to its peroxidase content and reaction with phenolic compounds. The residue contains an indole-acetic acid oxidase which is optimally active at the pH optimum for crocin destruction (pH 3·6); both activities are stimulated by 2,4-dichlorophenol. Catalase present in the preparation appears to have no influence on crocindestroying activity. Generation of hydrogen peroxide was not detected, although there is an absolute requirement for oxygen. The soluble fraction of the leaf contains a thermolabile factor which stimulates crocin destruction by the particulate system. Partial purification and resolution of this factor into several fractions by ion-exchange chromatography is accompanied by purification and fractionation of peroxidase activity. It is concluded that crocin is destroyed by an aerobic oxidation mediated by peroxidase, although the exact requirements for the reaction have not been established. Evidence is presented to support the claim that the particulate system participates in the loss of carotene which occurs when sugar beet leaves are damaged.