Purification and properties of a β-galactosidase from carambola fruit with significant activity towards cell wall polysaccharides

• Published in: Phytochemistry (Oxford) 2005, Vol.66 (2), p.153-163
• Main Authors: Balasubramaniam, Sumathi, Lee, Heng Chin, Lazan, Hamid, Othman, Roohaida, Ali, Zainon Mohd
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; amino acid sequences; Averrhoa carambola; Averrhoa carambola L; beta-galactosidase; beta-Galactosidase - chemistry; beta-Galactosidase - isolation & purification; beta-Galactosidase - metabolism; Biological and medical sciences; Cell Wall - metabolism; cell wall components; Cell wall modification; enzyme activity; Enzyme purification and properties; Enzymes; Fruit; Fruit - enzymology; fruits (plant anatomy); Fundamental and applied biological sciences. Psychology; galactans; glycosylation; hemicellulose; Isoenzymes; isozymes; Magnoliopsida - enzymology; Metabolism; Molecular Sequence Data; Oxalidaceae; pectins; Pectins - metabolism; Plant physiology and development; plant proteins; polypeptides; polysaccharides; Polysaccharides - chemistry; Polysaccharides - metabolism; ripening; Sequence Homology, Amino Acid; structure-activity relationships; Substrate Specificity; β-Galactosidase
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/j.phytochem.2004.11.005

Four β-galactosidase isoforms (β-gal I, II, III, IV) were isolated from ripe carambola fruit and β-gal I, the predominant isoform, was purified to electrophoretic homogeneity and the properties is reported. β-Galactosidase (EC. 3.2.1.23) from ripe carambola ( Averrhoa carambola L. cv. B10) fruit was fractionated through a combination of ion exchange and gel filtration chromatography into four isoforms, viz. β-galactosidase I, II, III and IV. This β-galactosidases had apparent native molecular masses of 84, 77, 58 and 130 kDa, respectively. β-Galactosidase I, the predominant isoform, was purified to electrophoretic homogeneity; analysis of the protein by SDS–PAGE revealed two subunits with molecular masses of 48 and 36 kDa. N-terminal amino acid sequence of the respective polypeptides shared high similarities albeit at different domains, with the deduced amino acid sequence of certain plant β-galactosidases, thus, explaining the observed low similarity between the two subunits. β-Galactosidase I was probably a heterodimer that have glycoprotein properties and a p I value of 7.2, with one of the potential glycosylation sites appeared to reside within the 48-kDa-polypeptide. The purified β-galactosidase I was substantially active in hydrolyzing (1 → 4)β-linked spruce and a mixture of (1 → 3)β- and (1 → 6)β-linked gum arabic galactans. This isoform also had the capability to solubilize and depolymerize structurally intact pectins as well as to modify alkaline-soluble hemicelluloses, reflecting in part changes that occur during ripening.