Preparation and Some Properties of Active Monomer of Sweet Potato β-Amylase

Sweet potato β-amylase was divided into two active fractions (named F-A and F-B) by modification with periodate-oxidized maltohexaose at pH 9.7. F-A and F-B isolated by exclusion chromatography using Sephadex G-200 corresponded to a pentamer of the enzyme with molecular weight of 31.5 × 10 4 and a monomer with molecular weight of 6.4 × 10 4 , respectively. The contents of carbohydrate of the modified enzymes were 9.7% for F-A and 9.3% for F-B. The specific activities of F-A and F-B were 2,059 and 1,129 units/mg of protein and were reduced to 82% and 45% of that of the original enzyme, respectively. The modification of the enzyme with the oxidized maltohexaose was due to formation of a Schiff base between ε-NH 2 groups of lysines of the enzyme protein and CHO groups of the oxidized maltohexaose.