Debranching Enzymes of Potato Tubers (Solanum tuberosum L.). I. Purification and Some Properties of Potato Isoamylase

Abstract

Potato tubers contain 3 debranching enzymes separable by polyacrylamide gel electrophoresis. One of them, isoamylase, has been purified to apparent homogeneity on disc gel electrophoresis by isoelectric precipitation, fractionation with ammonium sulfate, gel filtration on Sepharose 6B and finally affinity chromatography on Sepharose 4B-soluble starch, successively. The purified enzyme has a specific activity of 8.0U/mg of protein. It hydrolyzes the α-1, 6-glucosidic bonds in glycogen and phytoglycogen not only as rapidly as those in amylopectin but also completely, but cannot hydrolyze pullulan. From these results potato isoamylase was found to have the same substrate specificity as that of Pseudomonas isoamylase. However, different from the latter, it has an optimum pH of 5.5-6.0, optimum temperature of 50°C and was reversibly inactivated by p-chloromercuri-benzoate.