The highly humid climate of Japan facilitates the growth of various molds. Among these molds,
Aspergillus oryzae is the most important and popular in Japan, and has been used as yellow-koji in
producing many traditional fermented beverages and foods, such as Japanese sake, and soy
sauce. Taka-amylase A (TAA), a major enzyme produced by the mold, is well known worldwide to
be a leading enzyme for industrial utilization and academic study, since many extensive studies
have been carried out with TAA. In southern Kyushu, the other koji’s of citric acid-producing
molds have often been used, such as in the production of a traditional distilled liquor of shochu.
The koji molds black-koji and white-koji produce two types of α-amylase, namely, acid-stable
(AA) and common neutral (NA). The latter enzyme is enzymatically and genetically similar to
TAA. In this review, we investigate AA from three molds, Aspergillus niger, A. kawachii and A.
awamori, and the yeast Cryptococcus sp. regarding the distinguishable properties between AA and
NA. (i) The N-terminus amino acid sequences of AA determined by molecular cloning started with
the sequence of L-S-A-, whereas those of NA started with A-T-P-. (ii) Most of the full sequences of
AA were composed of, besides a core catalytic domain, an extra domain of a hinge region and a
carbohydrate binding domain, which could be responsible for raw-starch-digestibility. The AA from
A. niger has no exceptionally extra domain, similarly to NA. (iii) Simple methods for distinguishing
AA from NA using CNP-α-G3 and G5 as substrates were developed by our group. (iv) The
number of subsite in AA on the basis of its cleavage pattern of maltooligosaccharides was estimated
to be five, which differs from that of TAA, 7–9. AA has many advantages in industrial applications,
such as its acid-stability, thermostability, and raw-starch digesting properties.