Purification and molecular properties of an α-galactosidase synthesized and secreted by Aspergillus nidulans Free

α-Galactosidases from mycelial extract and culture filtrate of Aspergillus nidulans have been purified to homogeneity and utilised to obtain polyclonal antibodies anti-α-galactosidase. The enzymatic characteristics and the cross reactivity of the antibodies suggest that α-galactosidases isolated from the two sources were the same enzyme. Thus, A. nidulans synthesized and secreted only one enzymatic form of α-galactosidase which is a multimeric enzyme of 370 kDa composed of four monomers of 87 kDa and a pI of 6.3. The optimum temperature of activity was 50°C and the optimum pH 4–5. The enzyme was stable over a wide range of pH but quite unstable to temperature. α-Galactosidase of A. nidulans is a very specific enzyme, it is active only on p-nitrophenyl-α-D-galactoside (PNPG), melibiose and raffinose. When PNPG was utilised as substract melibiose, raffinose, galactose and glucose were competitive inhibitors of the activity.