A strain of Micromonospora sp. produced a new substance capable of inhibiting β-glucuronidase activity. The inhibitor, abbreviated as M-GCI, was purified by means of ethanol treatment, column chromatography on DEAE-cellulose, and gel filtration on Sephadex G-50 from the culture filtrate, and properties of the purified preparation have been investigated. M-GCI is a glycoprotein which has a molecular weight of about 8, 700. The protein constituents lack S-containing and basic amino acids. The inhibitory activity of M-GCI was sensitive to pH. It was stable in the alkaline pH range, but gradually lost its inhibitory activity as the acidity increased. M-GCI showed strong inhibition against β-glucuronidase from Escherichia coli and a-glucosidase from yeast. Since MGCI showed little effect on β-glucuronidase from bovine liver, the inhibitory action of M-GCI seemed to be rather specific for the β-glucuronidase from E. coli. These properties have proved that M-GCI is completely different from the other inhibitors of β-glucuronidase so far reported.

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