Purification and characterization of Endo-1,4-β- D-galactanases from Aspergillus niger and Aspergillus aculeatus: Use in combination with arabinanases from Aspergillus niger in enzymic conversion of potato arabinogalactan

• Published in: Carbohydrate polymers 1991, Vol.16 (2), p.167-187
• Main Authors: van de Vis, J.W., Searle-van Leeuwen, M.J.F., Siliha, H.A., Kormelink, F.J.M., Voragen, A.G.J.
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Biotechnology; Food industries; Fruit and vegetable industries; Fundamental and applied biological sciences. Psychology
• ISSN: 0144-8617; 1879-1344
• DOI: 10.1016/0144-8617(91)90101-H

Two galactanases, purified from experimental enzyme preparations derived from Aspergillus niger and Aspergillus aculeatus were found to be similar in a number of properties. They had similar molecular weights (M r = 42–43 kD) and both showed highest activity on 1,4-β- D-galactan. Optimal activity was measured at 50–55°C and pH 4·00–4·25; optimal stability was observed in the pH range of 5–7 at 30°C. A sodium acetate buffer was found to be the best incubation buffer. Activity and stability were affected by Pb 2+ ( endo-galactanase from A. aculeatus was inhibited completely) and to a lesser extent by Ag + and Zn 2+ ions. Digestion of (arabino)-1,4-β- D-galactan resulted initially in a big shift in the M w value of the bulk of (arabino)-1,4-β- D-galactan and formation of low galacto-oligomers, mainly tetra- and trimers of galactose. In the final stage of the reaction mono- and dimer accumulated as end products. Therefore a multiple attack mechanism was suggested for the endo-1,4-β- D-galactanases. The galactanases did not hydrolyse arabino-1,3/6-β- D-galactan. The effect of the temperature on their stability, their specific activities and their affinity for potato arabinogalactan differed; in the absence of substrate the A. niger and A. aculeatus endo-galactanase were stable up to 60°C and 35°C, respectively. The specific activities on potato arabinogalactan in a sodium acetate buffer pH 5·0, 30°C were found to be 158 and 244 u/mg, respectively. The K m values estimated for potato arabinogalactan were 0·77 and 0·31 g/litre, respectively. For an optimal breakdown of potato arabinogalactan combined action of arabinanases from A. niger and endo-galactanase was required. Arabinofuranosidase B did not stimulate the degradation of potato arabinogalactan by the endo-galactanases under the conditions used, whereas endo-1,5-α- L-arabinanase had an immediate synergistic effect with both endo-galactanases, indicating the presence of linear 1,5-α- L-arabinan side chains.