Catalytic mechanism of enzymic glycosyl transfer

Inversion of configuration during hydrolysis of α‐1,4‐galacturonidic linkage by three Aspergillus polygalacturonases

“…It is well established that enzymes hydrolyzing glycosidic linkages of glycosides, oligosaccharides and polysaccharides utilize two different reaction mechanisms that lead to a different configuration of the newly formed reducing end [1][2][3]. Enzymes catalyzing the hydrolysis in one chemical step, the so-called single displacement mechanism, generate reducingend products with a configuration of the anomeric carbon reversed to that of the cleaved glycosidic linkage.…”

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“…Ever since the structure of lysozyme was determined 1 , the enzyme mechanisms of glycosyl hydrolases and transferases have aroused wide interest [2][3][4] . Using similar chemical principles, these enzymes process a wide variety of carbohydrate polymers, many of which are important as nutrients, cell wall components or signal transmitters 5 .…”

Fungal trehalose phosphorylase: kinetic mechanism, pH-dependence of the reaction and some structural properties of the enzyme from Schizophyllum commune

“…Table 2 (superscripts p and s denote phospholysis and synthesis respectively). The free energies at 30 mC were calculated using the relationship ∆G l RT ln [(k B T/h)/k 1st ], and a value of 6.313i10 12 state of 1 M been chosen for all reactant concentrations, the result would have been the opposite. The data also allow us to assign the largest free-energy barrier of the overall reaction to the transformation of E:Glc 1-P and -glucose into E:P i and α,α-trehalose.…”

“…The stereochemical outcome of the overall chemical reaction in eqn (1) is one of retention of configuration at C-1 of α,α-trehalose and Glc 1-P ; glucosyl transfer with retention is a characteristic feature of enzymes of family GT-4. By analogy with retaining glycosidases, for which a large body of mechanistic and structural information is available (for a review, see [11]), α-retaining glucosyl transfer to and from phosphate is anticipated to occur through a double-displacement mechanism that involves two configurationally invertive steps (reviewed in [11,12]) : (1) cleavage of the carbon-oxygen bond of the glucosyl donor and formation of a covalent β-glucosyl-enzyme intermediate ; and (2) reaction of the intermediate with phosphate to yield Glc 1-P. Phospholysis of sucrose by sucrose phosphorylase is a well characterized example of the α-retaining phosphorylase mechanism [13], and the kinetics of this enzymic reaction are Ping Pong Bi Bi. Unlike sucrose phosphorylase, and unusually for a retaining GT, fungal trehalose phosphorylase follows a ternarycomplex kinetic mechanism in which both substrates must bind to the enzyme before a product is released [2].…”