title: Purification and properties of coffee-bean alpha-D-galactosidase.
abstract: A purification method for alpha-D-galactosidase from Coffea canephora is described. Two enzymes, alpha-D-galactosidases I and II, having molecular weights of 28,000 and 36,500, respectively, were found and extensively purified. The reaction mechanism of alpha-D-galactosidase II was studied. The enzyme hydrolyzed aryl and alkyl alpha-D-galactopyranosides and was severely inhibited by excess of these substrates. No inhibition occurred with raffinose. The influence of para substituents on the reaction rate of phenyl alpha-D-galactopyranosides, the effect of added alcohols, and the non-competitive inhibition by methyl alpha-D-galactopyranoside were investigated. A two-step mechanism with the formation of an enzyme-galactosyl complex is proposed. With aryl galactopyranosides, the reaction of the enzyme-galactosyl complex with water is rate-limiting. Influences of the substituents on the inhibition constant were investigated by linear free-energy relationships, and significant correlations between this constant and electronic parameters could be calculated. The influence of pH on the reaction is complex.
mesh_terms: D000535:Aluminum; D002845:Chromatography; D002850:Chromatography, Gel; D003069:Coffee / Q000201:enzymology; D004355:Drug Stability; D005696:Galactosidases / Q000302:isolation & purification / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000302:isolation & purification / Q000378:metabolism; D007700:Kinetics; D008433:Mathematics; D008970:Molecular Weight; D012639:Seeds / Q000201:enzymology*
chemical_list: D003069:Coffee; D007527:Isoenzymes; D000535:Aluminum; D005696:Galactosidases