Ascorbic acid oxidase of Myrothecium verrucaria

Abstract

Ascorbic acid oxidase is widely distributed in higher plants. The enzyme from certain tissues has been highly purified, and some of its properties are well established, especially its copper protein character (6, 19, 23, 24). The function of the enzyme and the role and metabolism of ascorbic acid in plant tissues has been studied extensively (19). Although enzymatic pathways of electron transfer between dehydrogenase systems and ascorbic acid are known, the significance of these and of ascorbic acid oxidase, itself, in respiration or other metabolic phenomena remains obscure. Two atypical ascorbic acid oxidases in lower plants have been investigated, one by Mandels (17, 18) in spores of the fungus Myrothecium verrucaria, the other by Ward (29) in the slime mold Physarum polvcephalunii. These enzymes were termed "atypical" because they differed from the copper enzyme in response to inhibitors of metallo-enzymes, in reaction products, or in substrate specificity. Furthermore, the slime mold enzyme appeared to require an intermediate thiol compound for activity. The mycelium of M. verrucaria also contains an atypical ascorbic acid oxidase (18,30) with certain properties distinctly different from those of the spore enzyme as well as the slime mold and higher plant oxidases. The present study deals mainly with the general properties and cellular location of the mycelial oxidase and its role as an electron transfer agent in the respiration of mycelium.