In C. murisepticum, alpha-galactosidase (EC 3.2.1.22) was induced during growth in the presence of melibiose or raffinose, and to a much lesser extent in the presence of galactose, as a single carbon source. Evidence was obtained to show that the enzymes induced by any of the sugars were identical with one another. The principal inducer of C. murisepticum alpha-galactosidase is melibiose. Rffnnose elicits induction only indirectly by prior extracellular hydrolysis to melibiose. The enzyme was

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... rified to homogeneity from melibiose-grown cells by column chromatographic fractionation of cell-free extract on Sephadex G-200, followed by that on QAE-Sephadex A-25, and finally by ultracentrifugation in a 5-20% sucrose density gradient. The purified C. murisepticum alphagalactosidase is a homotetramer of 320 kDa molecular mass, with a Km for melibiose, 2 mM; for p-nitrophenyl-alpha-D-galactopyranoside (PNPG), 0.17 mM; and pH optimum of 7.5. Under optimal conditions of induction, 2% of total protein synthesized by C. murisepticum cells was alphagalactosidase (as determined by selective immunoprecipitation of radiolabelled enzyme protein). The enzyme alpha-galactosidase (EC 3.2.1.22) hydrolyzes terminal nonreducing alpha-D-galactose residues in alpha-galactosides and galactose containing oligosaccharides, e.g., melibiose, raffinose, stachyose, and verbascose, which are widely distributed in nature (3). Biochemical and genetic aspects of alpha-galactosidase induction, which may shed light on certain intriguing modes of melibiose and raffinose utilization, have so far been studied in only a few microorganisms.