Glucosylation kinetics

The non-linear dependence of the relaxation process on the DNA concentration was also observed in stopped-flow experiments and the same mechanism, i.e. fast pre-equilibrium followed by a slow intercalation step, was proposed." This latter study did not report values for the individual rate constants. The mechanism proposed in Scheme 4 was employed in subsequent studies despite the criticism on the accuracy for the data related to the fast kinetic component (see below). The original temperature jump study also showed that the relaxation kinetics depend on the structure of the DNA.117 The slower intercalation rate for 5 with T2 Bacteriophage DNA when compared to ct-DNA was ascribed to the glucosylation of the former DNA (Table 3). 

Kinetics of Glucosylation. The detailed kinetic analysis of the partially purified enzyme (44) was consistent with an ordered bi bi mechanism, where UDP-glucose binds to the enzyme first, followed by the flavonoid aglycone... 

The teichoic acid shows an infrared absorption band at 1751 cm.-1, characteristic of carboxylic ester groups, which is not observed in samples from which the D-alanine residues have been removed. Removal of the u-alanine was readily effected with ammonia or hydroxylamine, when D-alaninamide or D-alanine hydroxamate were formed. The kinetics of the reaction with hydroxylamine reveal the high reactivity of its D-alanine ester linkages, which, like those in most other teichoic acids, are activated by the presence of a neighboring phosphate group. That the D-alanine residue is attached directly to the ribitol residues, instead of to the d-glucosyl substituents, was also shown by oxidation with periodate under controlled conditions of pH, when it was found that the D-alanine residues protect the ribitol residues from oxidation. Under the same conditions, all of the ribitol residues were oxidized in a sample of teichoic acid from which the D-alanine had been removed, and it is concluded that the ester groups are attached to C-2 or C-3 of the ribitol residues. 

The kinetic isotope effects Might/Mieavy, for the hydrolysis at pH 6.0 of a-glucosyl fluoride at 80 °C and /J-glucosyl fluoride at 50 °C, isotopically substituted as shown in structure 352, have been found381 to be as follows ... 

The glycogen debranching enzyme is the first bifunctional eukaryotic enzyme to be reported that consists of a single polypeptide chain. It catalyzes two distinct activities an oligosaccharide frons-glycosylation followed by hydrolysis of an (1—> 6)-linked D-glucosyl unit to liberate free glucose. Physical-chemical and kinetic characterization of this novel bifunctional enzyme is described by Nelson. 

Cartwright AM, Lim EK, Kleanthous C, Bowles DJ (2008) A Kinetic Analysis of Regios-pecific Glucosylation by Two Glycosyltransferases of Arabidopsis thaliana Domain Swapping to Introduce New Activities. J Biol Chem 283 15724... 

The dotted lines are meant to convey a minimal degree of covalent bonding kinetic isotope effect data for hydrolysis of a-glucosyl fluoride were fitted to a transition state structure with bond orders to leaving group and nucleophile of only 0.001. 

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