4-Hydroxycinnamic Acid Hydroxylase and Polyphenolase Activities in Sorghum vulgare1
AUTOR(ES)
Stafford, H. A.
RESUMO
Green shoots and first internodes of Sorghum vulgare var. Wheatland milo contain three phenoloxidase activities separable by means of Sephadex G-100 gel filtration. Two of these are found only in green leaves. I, eluted at the void volume and presumably a high molecular weight form, has both monophenol and diphenol oxidase functions; II, an intermediate molecular weight form displays only a diphenol function; III, a low molecular form found only in first internodes, catalyzes the hydroxylation of 4-hydroxycinnamic acid to caffeic acid and may have a weak diphenol activity. The hydroxylase activities of peaks I and III were completely inhibited by boiling or by 1 millimolar diethyldithiocarbamate and were partially inhibited by 1 millimolar KCN. The time courses of the two monophenol activities differ in that the activity of internode tissue was linear for at least 3 hours while that of the leaf began to decrease after 15 minutes. Both O2 and a suitable electron donor were obligatory. At pH 6, ascorbic acid and 2-amino-4-hydroxy-6, 7-dimethylpteridine were the best electron donors, while NADPH was less effective. The diphenol oxidase functions of forms I and II in leaf preparations were not identical. The activity of I was less stable than that of II. While both were more active with chlorogenic acid, the ratio of activity with chlorogenic acid to that with 3,4-dihydroxyphenylalanine was less than 50 for I and greater than 50 for II.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=366011Documentos Relacionados
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