No abstract

Two isozymes (F-IB and F-II) of phloroglucinol oxidase (PhO) in cabbage (Brassica oleracea L.) were purified from cabbage. The purified enzymes were found to be in a homogeneous state by polyacrylamide gel electrophoresis (PAGE) and sodium dodecyl sulfate (SDS)-PAGE. The molecular weights of F-IB and F-II were estimated to be ∼43 000 and 32 000, respectively, by SDS-PAGE. Both purified enzymes only oxidized 1,3,5-trihydroxybenzenes, such as phloroglucinol and phloroglucinolcarboxylic acid. Both enzymes also had strong peroxidase (POD) activity. The pH optima of PhO and POD of F-IB were 8.0 and 6.7, respectively, and those of F-II were 7.4 and 6.7, respectively. Activities of both F-IB and F-II were stable in the pH range 6−11 at 5 °C for 20 h, and were markedly inhibited by sodium diethyldithiocarbamate and potassium cyanide. MnCl2 markedly activated the PhO activity of F-IB and F-II, but strongly inhibited their POD activity. Keywords: Cabbage (Brassica oleracea L.); polyphenol oxidase; phloroglucinol oxidase; peroxidase; characterization