Abstract:  Aspergillus niger Sx,isolated from nature,could secrete raw-starch glucoamylase (RSAG)with high enzyme activity at level of 382u/g.After fermentation for 24 hours at 30℃in solid wheat bran culture ,the maximum secretion of RSAG was achieved at pH6.5 with the ratio of solid to water as 1∶1.6.Further,the enzymatic production was confirmed by paper chromatography as glucose.Interestingly,it was discovered that SDS could keep RSGA in its initial state.When the concentration in the crude enzyme was 6mg/ml,the activity of enzyme was kept intact and active after 10days storage at 30℃.Additionally,RSGA was purified initially by means of ammonium sulfate fractionation and dialysis.The optimum hydrolysis conditions for the purified enzyme were pH4.5,60℃.Amazingly,it preserved a high stabillity at pH between 4.0and 7.0,After incubation at 80℃ for 1 hour,the enzyme still retained 15% activity.Metal ions such as Ag+、Sn2+ and Hg2+ could inhibit the enzyme to different extents,where as EDTA、Ca+ showed effect on the activity of the enzyme.In contrast to the forenamed cation,Co2+ and K+ could stimulate the activity of enzyme slightly.

Key words:  , Raw Starch Glucoamylase Aspergillus niger Fermentation condition Enzyme character；