Characterization and biotechnological application of an acid α-galactosidase from Tachigali multijuga Benth. seeds

Abstract

Tachigali multijuga Benth. seeds were found to contain protein (364 mg g−1 dwt), lipids (24 mg g−1 dwt), ash (35 mg g−1 dwt), and carbohydrates (577 mg g−1 dwt). Sucrose, raffinose, and stachyose concentrations were 8.3, 3.0, and 11.6 mg g−1 dwt, respectively. α-Galactosidase activity increased during seed germination and reached a maximum level at 108 h after seed imbibition. The α-galactosidase purified from germinating seeds had an Mr of 38,000 and maximal activity at pH 5.0–5.5 and 50 °C. The enzyme was stable at 35 °C and 40 °C, but lost 79% of its activity after 30 min at 50 °C. The activation energy (Ea) values for p-nitrophenyl-α-d-galactopyranoside (pNPGal) and raffinose were 13.86 and 4.75 kcal mol−1, respectively. The Km values for pNPGal, melibiose, raffinose, and stachyose were 0.45, 5.37, 39.62 and 48.80 mM, respectively. The enzyme was sensitive to inhibition by HgCl2, SDS, AgNO3, CuSO4, and melibiose. d-Galactose was a competitive inhibitor (Ki = 2.74 mM). In addition to its ability to hydrolyze raffinose and stachyose, the enzyme also hydrolyzed galactomannan.