Extracellular Isoamylase Produced by the Yeast Lipomyces kononenkoae

A strain of the starch-converting yeast Lipomyces kononenkoae produced, when grown on starch, a debranching enzyme that proved to be an isoamylase (glycogen 6-glucanohydrolase; E.C. 3.2.1.68). So far, only bacteria have been found to produce extracellular isoamylases. The yeast isoamylase enhanced beta-amylolysis of amylopectin and glycogen and completely hydrolyzed these substrates into maltose when combined with a beta-amylase but had no action on dextran or pullulan. By isopropanol precipitation and carboxymethyl cellulose chromatography, L. kononenkoae isoamylase was partially purified from the supernatant of cultures grown on a mineral medium with soluble starch. Optimum temperature and pH for activity of the isoamylase were 30 degrees C and 5.6. The molecular weight was around 65,000, and the pI was at pH 4.7 to 4.8. The K(m) (30 degrees C, pH 5.5) for soluble starch was 9 g liter.