Acidic peroxidases from suspension­cultures of sweet potato

Abstract

We established an efficient production system of peroxidase (POD, EC 1.11.1.7) in cultured cells of sweet potato [Ipomoea batatas (L.) Lam. cv White Star]. A cell line SP-47 derived from cell suspension cultures of sweet potato produced a level of POD, i.e. ca 6800 units g？1 dry cell wt (substrate, pyrogallol) when 1 g (fr. wt) of cells was inoculated into 50 ml LS medium supplemented with 1 mg 1？1 2,4-D in a 300 ml conical flask and cultured at 25° in the dark (100 rpm) for 25 days. Three acidic POD isoenzymes (A-1, A-2 and A-3) were purified to homogeneity from suspension-cultured cells by DEAE-cellulose and gel filtration column chromatography. A major isoenzyme A-2, a monomeric hemoprotein Mr ca 40 000, pI: ca 4.5, RZ value: 4.1), occupied more than 7.5% of total protein in cultured cells and ca 88% of total POD activity. The Km values of isoenzyme A-2 for pyrogallol and H2O2 were 2.53 and 5.76 mM, respectively. RZ values for two minor isoenzymes A-1 (Mr ca 43 000, pI ca 5.0) and A-3 (Mr ca 40 000, pI (ca 6) were 1.9 and 1.6, respectively, which was quite low compared with isoenzyme A-2.