Hydrolyses of alpha- and beta-cellobiosyl fluorides by cellobiohydrolases of Trichoderma reesei.
Cellobiohydrolase II hydrolyses alpha- and beta-D-cellobiosyl fluorides to alpha-cellobiose at comparable rates, according to Michaelis-Menten kinetics. The stereochemistry, absence of transfer products and strict hyperbolic kinetics of the hydrolysis of alpha-cellobiosyl fluoride suggest that the mechanism for the alpha-fluoride may be the enzymic counterpart of the SNi reaction observed in the trifluoroethanolysis of alpha-glucopyranosyl fluoride [Sinnott and Jencks (1980) J. Am. Chem. Soc. 102, 2026-2032]. The absolute factors by which this enzyme accelerates fluoride ion release are small and greater for the alpha-fluoride than for the beta, suggesting that its biological function may not be just glycoside hydrolysis. Cellobiohydrolase I hydrolyses only beta-cellobiosyl fluoride, which is, however, an approx. 1-3% contaminant in alpha-cellobiosyl fluoride as prepared and purified by conventional methods. Instrumental assays for the various components of the cellulase complex are discussed.
Konstantinidis
A K
AK
Department of Chemistry, University of Illinois, Chicago 60680.
Marsden
I
I
Sinnott
M L
ML
D001665:Binding Sites; D002236:Carbohydrate Conformation; D002475:Cellobiose / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D043366:Cellulose 1,4-beta-Cellobiosidase; D004563:Electrochemistry; D005459:Fluorides / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D014242:Trichoderma / Q000201:enzymology*
C074099:cellobiosyl fluoride; D002475:Cellobiose; D006026:Glycoside Hydrolases; D043366:Cellulose 1,4-beta-Cellobiosidase; D005459:Fluorides