A β-l, 4-mannan hydrolyzing enzyme was isolated from an extract preparation of Koji culture of a strain of Asp. niger on wheat bran. After desalting through a column of Sephadex G-50, the enzyme was purified by chromatography on columns of DEAE-Toyopearl 650 S and calcium hydroxylapatite. The optimum pH of the purified enzyme on guar gum was about 5, but even at pH 7. 0, the enzyme showed the activity of 70 % of that at the opt. pH. The enzyme was relatively stable to heat and active at 60°C. The enzyme hydrolyzed locust bean gum, glucomannan, and guar gum and the maximum degrees of hydrolysis were 30, 25, and 15 %, respectively. In the hydrolysate of guar gum were found a trace amount of mannose and small amounts of bioses whose structures were mannobiose and Gal-16-Man. Several other oligosaccharides of trioses and those of more sugar residues were also observed. But, the major part of the hydrolysates of guar gum were those consisted of ten or more sugar residues . This result indicates that, though guar gum consists of 6 parts of mannose and 4 parts of galactose, the fine structure is far from those so far reported as a repeated structure of Gal-1, 6-β-Man-1, 4-Man where mannosidic linkages constitute the main chain. Experiments using rats revealed that supplying guar gum digests with above enzyme as a food additive results in decrease of total content of lipids including cholesterol and triglycer ides in the liver.
