beta-Glucosidase catalyzing specific hydrolysis of an iridoid beta-glucoside from Plumeria obtusa.
An iridoid beta-glucoside, namely plumieride coumarate glucoside, was isolated from the Plumeria obtusa (white frangipani) flower. A beta-glucosidase, purified to homogeneity from P. obtusa, could hydrolyze plumieride coumarate glucoside to its corresponding 13-O-coumarylplumieride. Plumeria beta-glucosidase is a monomeric glycoprotein with a molecular weight of 60.6 kDa and an isoelectric point of 4.90. The purified beta-glucosidase had an optimum pH of 5.5 for p-nitrophenol (pNP)-beta-D-glucoside and for its natural substrate. The Km values for pNP-beta-D-glucoside and Plumeria beta-glucoside were 5.04+/-0.36 mM and 1.02+/-0.06 mM, respectively. The enzyme had higher hydrolytic activity towards pNP-beta-D-fucoside than pNP-beta-D-glucoside. No activity was found for other pNP-glycosides. Interestingly, the enzyme showed a high specificity for the glucosyl group attached to the C-7' position of the coumaryl moiety of plumieride coumarate glucoside. The enzyme showed poor hydrolysis of 4-methylumbelliferyl-beta-glucoside and esculin, and did not hydrolyze alkyl-beta-glucosides, glucobioses, cyanogenic-beta-glucosides, steroid beta-glucosides, nor other iridoid beta-glucosides. In conclusion, the Plumeria beta-glucosidase shows high specificity for its natural substrate, plumieride coumarate glucoside.
Boonclarm
Doungkamol
D
Department of Biochemistry, Faculty of Science, Mahidol University, Bangkok 10400, Thailand.
Sornwatana
Thakorn
T
Arthan
Dumrongkiet
D
Kongsaeree
Palangpon
P
Svasti
Jisnuson
J
D029062:Apocynaceae / Q000201:enzymology*; D002384:Catalysis; D044602:Cellulases / Q000737:chemistry* / Q000378:metabolism; D003373:Coumaric Acids / Q000737:chemistry* / Q000378:metabolism; D006868:Hydrolysis; D057888:Iridoid Glucosides; D039823:Iridoids / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D013379:Substrate Specificity
D003373:Coumaric Acids; D057888:Iridoid Glucosides; D039823:Iridoids; C513191:plumieride coumarate glucoside; D044602:Cellulases