Ｂａｃｉｌｌｕｓ ｃｉｒｃｕｌａｎｓ Ｆ‐２の生産するアミラーゼとその生産調節機構について

Abstract

Bacillus circulans F-2 has three unique properties : it produced G6 preferentially from solu-ble starch in the early stage of hydrolysis ; it digested potato starch granules effectively ; and it produced some kinds of amylase only when raw starches were used as a carbon sources. Therefore, the amylase and regulation of its synthesis in this bacterium were studied. We newly purified two amylases (amylase I and III) that are different from a major amy-lase (amylase II), having potent raw starch-digesting activity. Amylase I hydrolyzed a-1, 4-glucosidic and a-1, 6-glucosidic linkages att the same rate. Enzymatic properties of amylase III were almost the same as that of amylase II. The physiological significance of amylase is that they act synergystically in digesting starch granules. Potato and corn starch granules were cross-linked by epichlorohydrin to various extents (degree of cross-linking, DC=0.6-7.1). Using these starches as a carbon source for the cul-tivation of this bacterium, production of amylase was investigated. CLP (cross-linking potato starch, DC =4.0) induced 0.6 U/ml of amylase, which is 1.8 times as much as that on raw potato starch. B. circulans F-2 was found to produce amylase on maltose or soluble starch media if it is grown in appropriate condition such as dialysis and feeding cultivation, i. e., condition to afford the low bacterial growth. Its amylase synthesis is inducible by maltooligosaccharides and severely repressed by glucose. High amylase production was always accompanied by low a-glucosidase production and the absence of glucose in culture broth. In the presence of 1-deoxynojirimycin (DNM), an inhibitor of a-glucosidase activity, the bacterium produced a significant amount of amylase even in batch cultivation on maltose. From these results, the regulation of amylase synthesis in B. circulans F-2 is affected by its high sensitivity to glucose repression and by the production of a-glucosidase which leads to the formation of glucose.