Digestive Enzyme of Tilapia-III. Purification and Properties of .Alpha.-Glucosidases from Tilapia Intestine.

Two alpha-glucosidases, I and II, of the intestine of Tilapia nilotica were purified by ammonium sulfate precipitation, followed by affinity chromatography (alpha-cyclodextrin-Sepharose 6B), gel filtration (Sephadex G-150), and chromatofocusing (poly exchanger PBE 94). Each of the two alpha-glucosidases was found to be in pure form when examined by electrophoresis.The specific activity of I was 27-fold of that of the crude extract, which was slightly higher than 21-fold for that of II. The enzymes I and II had molecular weights of 25,000 and 17,000 and showed the highest activity at a pH of 6.0 and at 55-degrees-C, respectively. Both enzymes were stable at pH 5.5-7.5 and below 60-degrees-C.The Km values for p-nitrophenyl-alpha-D-glucopyranoside of two enzymes, I and II, were calculated to be 2.61 and 1.65 mm, respectively.Both activities of the enzymes were inhibited by Hg2+ and DTNB. Both enzymes specifically digested maltose, maltotriose, maltotetraose, maltopentaose, and maltohexaose, but not amylose.