2001 Volume 48 Issue 2 Pages 187-193
In Kagoshima, citric acid and shochu are produced on a commercial basis by the koji of Aspergillus groups. The black Aspergillus groups are known to produce two types of a-amylase, the acid-stable and the neutral, besides glucoamylase. In this study, we purified the acid-stable enzyme (UAA) from the acidic extract of the citric acid koji, and studied some enzymatic properties, especially the action pattern towards maltooligosaccharides, by comparison with the neutral enzyme (UNA) from the koji. Product analysis showed that UAA demonstrated a distinct cleavage pattern towards oligosaccharides more than G4, which suggests that UAA has a different subsite structure from the ordinary neutral a-amylase such as Taka-amylase A. The number of subsite is estimated to be 5, and subsite affinities of Al, A2, and A5 were evaluated to be 1.2 kcal/mol, 1.4 kcal/mol and 2.1 kcal/mol. Experiments with chemical modification suggested that UAA has a residue of Leu instead of Lys209 on Taka-amylase A, and a residue of Glu instead of His2l0. A new substrate Gal-G3-CNP was enzymatically synthesized from lactose and G3-CNP in order to discriminate between the two a -amylases, the acid-stable and the neutral.