REGULATION OF PEROXIDASE-DEPENDENT OXIDATION OF PHENOLICS BY ASCORBIC-ACID - DIFFERENT EFFECTS OF ASCORBIC-ACID ON THE OXIDATION OF CONIFERYL ALCOHOL BY THE APOPLASTIC SOLUBLE AND CELL WALL-BOUND PEROXIDASES FROM EPICOTYLS OF VIGNA-ANGULARIS

Intercellular washing fluid (IWF) and washed cell walls obtained from epicotyls of Vigna angularis catalyzed the oxidation of coniferyl alco hol in the presence of hydrogen peroxide, indicating the presence of b oth soluble and bound peroxidases in the cell walls. The products of o xidation of coniferyl alcohol were identical in both cases. Ascorbic a cid inhibited the oxidation of coniferyl alcohol. The inhibition was d ue to the rapid reduction of an oxidized intermediate of coniferyl alc ohol by ascorbic acid, with resultant regeneration of coniferyl alcoho l. However, the inhibitory effects of ascorbic acid were different in the case of IWF and cell walls. Ascorbic acid completely inhibited the oxidation of coniferyl alcohol by IWF peroxidase as long as ascorbic acid was available, whereas the oxidation of coniferyl alcohol by cell wall-bound peroxidase was competitively inhibited by ascorbic acid. A scorbic acid was present in cell walls and lignin was formed in cell w alls during aging of stem. Based on these results, a possible function for ascorbic acid in the regulation of oxidation of phenolics in cell walls is discussed.