Biochemical and molecular characterization of glucoamylase produced by the Aspergillus niger strain HPD-2

Aspergillus niger HPD-2 has interesting growth characteris-tics, it grows at a temperature of 38 oC and pH of 3, it is also known to produce various enzymes of commercial interest such as glucoamylase, which is present in the medium even under non-inducible conditions and has important activity characteristics such as an optimum temperature of 70 oC and an optimum pH of 3-4. These features are very important be-cause they will help to minimize microbial contamination risk in industrial hydrolysis processes. For the characterization of A. niger HPD-2 glucoamylase, the presence and activity of the enzyme were verified in a non-inducing medium. The apparent kinetic parameters Km, Ki and Vmax were determined at 6.66 mM, 0.601 M and 66.5 mM/min, respectively, as well as its optimum pH and temperature activity (pH 3 and 70 degrees C). Comparatively speaking, these data are competitive against those reported for similar purified enzymes. On the other hand, DNA sequence analysis ofA. niger HPD-2 glucoamylase gene showed no changes in the promoter region or starch-binding domains. Therefore, the presence of the enzyme in a non-inducing medium could be related to changes in a repressor protein CreA.