Résumé
A strain of Rhizopus sp. screened among more than 800 filamentous fungi showed great ability to produce a thermostable alfa-amylase by solid state fermentation. The best production was obtained with a bran moisture content of 40 per cent when the enzyme activity reached 60 EU/g. of medium. During the purification procedures, a column of DEAE- Sephadex A-50 separeted the enzyme in two fractions and the larger (85 per cent of the total activity) showed optimum pH in a range from 4.0 to 5.6. Optimum temperature was found at 60-65§ C and in this range no loss of activity was observed after 60 min. of treatment in pH 5,0. Its Km and Vm are, respectively, of 5.0 mg/ml of starch and 10,01 uMol of reducing sugar/min./mg. of protein. Its molecular weight was calculated in 64.000 by gel filtration in Sephadex G-200. The dextrinization power of the enzyme was observed preferentialy on substrates compound by chain with higher ramifications, traht is: amylopectin > starch> amylose. Other aspects of the enzyme pattern action are also discussed