A. niger produced alpha-glucosidase, alpha-amylase and two forms of glucoamylase when grown in a liquid medium containing raw tapioca starch as the carbon source. The glucoamylases, which formed the dominant components of amylolytic activity manifested by the organism, were purified to homogeneity by ammonium sulfate precipitation, ion-exchange and two cycles of gel filtration chromatography. The purified enzymes, designated GA1 and GA2, a raw starch digesting glucoamylase, were found to have molar masses of 74 and 96 kDa and isoelectric points of 3.8 and 3.95, respectively. The enzymes were found to have pH optimum of 4.2 and 4.5 for GA1 and GA2, respectively, and were both stable in a pH range of 3.5-9.0. Both enzymes were thermophilic in nature with temperature optimum of 60 and 65 degrees C, respectively, and were stable for 1 h at temperatures of up to 60 degrees C. The kinetic parameters Km and V showed that with both enzymes the branched substrates, starch and amylopectin, were more efficiently hydrolyzed compared to amylose. GA2, the more active of the two glucoamylases produced, was approximately six to thirteen times more active towards raw starches compared to GA1.

School of Biological Sciences Universiti Sains Malaysia Penang Malaysia

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Anal Biochem. 1984 Nov 1;142(2):421-36 PubMed

Nature. 1970 Aug 15;227(5259):680-5 PubMed

Appl Environ Microbiol. 1983 Mar;45(3):905-12 PubMed

Biotechnol Bioeng. 1989 Jan 5;33(1):72-8 PubMed

Arch Biochem Biophys. 1969 Nov;134(2):539-53 PubMed

Biochemistry. 1971 Jun 22;10(13):2606-17 PubMed

Folia Microbiol (Praha). 1994;39(5):392-8 PubMed

Ann N Y Acad Sci. 1964 Dec 28;121:404-27 PubMed

Indian J Exp Biol. 1977 Jun;15(6):495-6 PubMed

J Biochem. 1981 Jan;89(1):125-34 PubMed

J Biochem. 1978 Nov;84(5):1183-94 PubMed