Purification and properties of an alpha-D-galactoside galactohydrolase from the seeds of Trifolium repens (white clover)

Abstract

Five alpha-D-galactosidases (alpha-D-galactoside galactohydrolase; EC 3.2.1.22) have been identified by chromatography and polyacrylamide-disc-gel electrophoresis in the germinated seeds of Trifolium repens (white clover). alpha-Galactosidase I has been purified to homogeneity with an approx. 2000-fold increase in specific activity. The enzyme was purified by a procedure which included precipitation by dialysis against citrate/phosphate buffer, pH3.5; (NH4)2SO4 precipitation; hydroxyapatite, DEAE-cellulose and ECTEOLA-cellulose column chromatography. Each stage of purification was controlled by polyacrylamide-disc-gel electrophoresis; the purified enzyme showed a single protein band that corresponded to the alpha-D-galactosidic activity. The pH optimum was found to be between pH 3.8 and 4.2; the enzyme is highly thermolabile. Hydrolysis of oligosaccharides and galactomannans has been examined, and it has been found that alpha-galactosidase I exhibits two enzymic activities, namely alpha-D-galactoside galactohydrolase and galactosyltransferase. By the polyacrylamide-gel-electrophoresis method of Hendrick & Smith (1968), and by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, the mol.wt. has been estimated to be 43 000 and 41 000 respectively. These results indicate that alpha-galactosidase I is a monomeric protein and that both enzymic activities associated with the enzyme reside on the same polypeptide chain.