Kinetic investigation of the substrate specificity of the cyanogenic beta-D-glucosidase (linamarase) of white clover.
Partially purified linamarase from Trifolium repens (genotype Lili acac) plants was kinetically characterized. Kinetic evidence was found to support the assumption that this cyanogenic beta-D-glucosidase has a broad substrate spectrum. p-Nitrophenyl-beta-D-xylopyranoside and p-nitrophenyl-alpha-L-arabinopyranoside substrates bound almost as tightly to the active center of the enzyme as the glucono(1----5)lactone transition-state analog inhibitor. Substrate specificity investigation also indicated that positions C-4 and C-6 on the pyranoside ring play an essential role in both substrate orientation and splitting. Recently very similar kinetic characteristics were reported on some mammalian cytosolic beta-D-glucosidases and a possible physiological interpretation of this coincidence is discussed. Inhibition studies with glucono(1----5)lactone revealed that the carbohydrate moiety of each substrate attached to the same binding site in the active center. Inhibition experiments with 1-thio substrate analogs demonstrated that the aglycon and the angular arrangement around the glycosidic linkage were the major determinants in the observed substrate specificity.
Pócsi
I
I
Institute of Biochemistry, Lajos Kossuth University, Debrecen, Hungary.
Kiss
L
L
Hughes
M A
MA
Nánási
P
P
D001667:Binding, Competitive; D002850:Chromatography, Gel; D003486:Cyanides / Q000378:metabolism; D005959:Glucosidases / Q000378:metabolism*; D007700:Kinetics; D007783:Lactones / Q000378:metabolism; D010944:Plants / Q000201:enzymology*; D013379:Substrate Specificity; D013438:Sulfhydryl Compounds; D001617:beta-Glucosidase / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*
D003486:Cyanides; D007783:Lactones; D013438:Sulfhydryl Compounds; D005959:Glucosidases; D001617:beta-Glucosidase