Inhibition of β-Galactosidase by Galactostatin, Galactostatin-Lactam, and 1-Deoxygalactostatin

Abstract

Galactostatin obtained from the fermentation broth of Streptomyces lydicus PA-5726 strongly inhibited β-galactosidase. Its derivatives, galactostatin-lactam and 1-deoxygalactostatin, were also inhibitors. Galactostatin and 1-deoxygalactostatin were fully competitive inhibitors with high affinities for Penicillium multicolor β-galactosidase, and their Ki values were 4.0 × 10-9 and 3.3 × 10-8 at pH 6.0, respectively, using ONPG as substrate. In their presence, the steady-state velocities of the enzyme were reached in a matter of minutes. Galactostatin-lactam, in contrast, showed no detectable lag time on interaction with the enzyme, and the type of inhibition was also competitive with a Ki value of 1.3 × 10-5 M. These three inhibitors bound to the enzyme in the same molar ratio (1:1). © 1988, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.