The glucosylamine oxidation pathway of vitamin C recycling.

The proposed glucosylamine oxidation pathway (GOP) is a two-step, intraerythrocyte, thermodynamically favorable nonenzymatic reaction that first binds glucose to the N-terminal valine of beta globin (βVal1) to form a closed-chain glucosylamine that can spontaneously reduce oxidized vitamin C to its antioxidant form. This review summarizes analytical, biochemical and clinical research supporting the existence of the GOP and the surprising hypothesis that βVal1 glucosylamine is a reducing agent that works cooperatively with reduced glutathione to dynamically regulate vitamin C recycling during naturally occurring periods of transiently or chronically elevated blood glucose and oxidant production. Rationale for the existence of the GOP is presented from the perspective of the hemoglobin glycation index, a clinically practical biomarker of risk for chronic vascular disease that we propose is mechanistically explained by person-to-person variation in GOP activity.

Electrostatic Control of Macrocyclization Reactions within Nanospaces.

The intrinsic structural complexity of proteins makes it hard to identify the contributions of each noncovalent interaction behind the remarkable rate accelerations of enzymes. Coulombic forces are evidently primary, but despite developments in artificial nanoreactor design, a picture of the extent to which these can contribute has not been forthcoming. Here we report on two supramolecular capsules that possess structurally identical inner-spaces that differ in the electrostatic potential (EP) field that envelops them: one positive and one negative.

Solvent and α-secondary kinetic isotope effects on β-glucosidase.

β-Glucosidase from sweet almond is a retaining, family 1, glycohydrolase. It is known that glycosylation of the enzyme by aryl glucosides occurs with little, if any, acid catalysis. For this reaction both the solvent and α-secondary kinetic isotope effects are 1.

N-phenylglucosylamine hydrolysis: a mechanistic probe of β-glucosidase.

The spontaneous hydrolysis of glycosylamines, where the aglycone is either a primary amine or ammonia, is over a hundred million-times faster than that of O- or S-glycosides. The reason for this (as pointed out by Capon and Connett in 1965) is that, in contrast to the mechanism for O- or S-glycoside hydrolysis, hydrolysis of these N-glycosides (e.g.

Methyl glucoside hydrolysis catalyzed by beta-glucosidase.

Sweet almond beta-glucosidase is a retaining, family 1, glycohydrolase, catalyzing the highly efficient hydrolysis of a variety of glycosides. For example, the enzyme-catalyzed hydrolysis of methyl beta-D-glucopyranoside is approximately 4 x 10(15)-times faster than the spontaneous hydrolysis at 25 degrees C. As with most enzymes, the dependence of k(cat)/K(m) on pH is bell-shaped, indicating the importance of a protonated (acidic) residue and a deprotonated (nucleophilic) residue in its mechanism.

Salt effects on beta-glucosidase: pH-profile narrowing.

Salts inhibit the activity of sweet almond beta-glucosidase. For cations (Cl(-) salts) the effectiveness follows the series: Cu(+2), Fe(+2)>Zn(+2)>Li(+)>Ca(+2)>Mg(+2)>Cs(+)>NH(4)(+)>Rb(+)>K(+)>Na(+) and for anions (Na(+) salts) the series is: I(-)>ClO(4)(-)>(-)SCN>Br(-) approximately NO(3)(-)>Cl(-) approximately (-)OAc>F(-) approximately SO(4)(-2). The activity of the enzyme, like that of most glycohydrolases, depends on a deprotonated carboxylate (nucleophile) and a protonated carboxylic acid for optimal activity.

Thioglycoside hydrolysis catalyzed by beta-glucosidase.

Sweet almond beta-glucosidase (EC 3.2.1.

Multiple sugar binding sites in alpha-glucosidase.

Twenty-five analogs of D-glucose were examined as reversible inhibitors of yeast alpha-glucosidase (EC 3.2.1.