Purification and properties of a beta-galactosidase from carambola fruit with significant activity towards cell wall polysaccharides.
beta-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. beta-galactosidase I, II, III and IV. This beta-galactosidases had apparent native molecular masses of 84, 77, 58 and 130 kDa, respectively. beta-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 beta-galactosidases, thus, explaining the observed low similarity between the two subunits. beta-Galactosidase I was probably a heterodimer that have glycoprotein properties and a pI value of 7.2, with one of the potential glycosylation sites appeared to reside within the 48-kDa-polypeptide. The purified beta-galactosidase I was substantially active in hydrolyzing (1-->4)beta-linked spruce and a mixture of (1-->3)beta- and (1-->6)beta-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.
Balasubramaniam
Sumathi
S
Faculty of Science and Technology, School of BioSciences and Biotechnology, Universiti Kebangsaan Malaysia, 43000 Bangi, Selangor, Malaysia.
Lee
Heng Chin
HC
Lazan
Hamid
H
Othman
Roohaida
R
Ali
Zainon Mohd
ZM
D000595:Amino Acid Sequence; D002473:Cell Wall / Q000378:metabolism*; D005638:Fruit / Q000201:enzymology*; D007527:Isoenzymes; D019684:Magnoliopsida / Q000201:enzymology*; D008969:Molecular Sequence Data; D010368:Pectins / Q000378:metabolism; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D001616:beta-Galactosidase / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism*
D007527:Isoenzymes; D011134:Polysaccharides; C007916:hemicellulose; D010368:Pectins; D001616:beta-Galactosidase