Extracellular alpha-amylase from Streptomyces rimosus.

A purification procedure for an extracellular alpha-amylase from Streptomyces rimosus, oxytetracycline-producing strain, is described. The enzyme obtained was shown to be an acidic (pI 4.75) monomer with a relative molecular mass (M(r)) of 43,000, containing three cysteines involved in the catalytic activity of the enzyme. Its amino-terminal part has 57-67% homology with amylases from other Streptomyces species. S. rimosus alpha-amylase is sensitive to higher temperatures, and partially stabilized by Ca2+ ions. It hydrolyses starch (optimum at pH 5.0-6.0) in an endohydrolase manner giving rise to maltotriose, maltotetraose and higher oligosaccharides. Starch granules, except those from rice, were not significantly affected by the isolated alpha-amylase.