Galactosyltransferase from buffalo milk: Further characterization

Buffalo milk galactosyltransferase is a single poly-peptide of molecular weight 55,000 to 56,000. The enzyme is specific for glucose as an acceptor substrate in the presence of 8-lactalbumin, L-Arabinose. L-xylose, D-ribose and D-fructose did not serve as acceptor substrates even at concentration as high as 0.13 M, while N-acetylglucosamine and ovalbumin served as good acceptors of galactosyl moiety in the absence of ∞ -lactalbumin. UDP-galacturonic acid did not serve as a donor substrate; on the contrary, it inhibited the reaction. Lactose synthetase reaction was inhibited by D-ribose, L-arabinose and L-xylose, whereas D-fructose did not show any inhibition. Buffalo milk ∞ -lactalbumin enhanced the synthesis of lactose but inhibited the synthesis of N-acetyllactosamine. Cations like Ca²⁺, Mg²⁺, Cu²⁺, Ba²⁺ and Co²⁺ could not replace Mn²⁺ in the N-acetyllactosamine synthetase reaction. Except Co²⁺, these cations had no effect on this reaction. Co²⁺ was found to be a competitive inhibitor of Mn²⁺. The observed inhibition of the reaction by-EDTA also confirmed the absolute requirement of Mn²⁺ for the reaction. Lactose synthetase reaction had an optimum pH of 8.5, whereas N-acetyllactosamine synthetase reaction was maximal at pH 8.0.