Substrate specificities and mechanism of action of multiple α-galactosidases from Streptomyces griseoloalbus

α-Galactosidase or melibiase is a versatile enzyme with many potential biotechnological and industrial applications. The substrate specificities of three α-galactosidases – α-Gal I, α-Gal II, and α-Gal III – from Streptomyces griseoloalbus were studied using different galactose-containing natural substrates like melibiose, raffinose and stachyose. The kinetic parameters Km and Vmax were determined from the Lineweaver–Burk plot. α-Gal I showed highest affinity towards melibiose where as α-Gal II and α-Gal III showed highest affinity towards stachyose. The 1H NMR studies showed that all the three α-galactosidases had a retaining mechanism of hydrolysis.