Catalysis by organic phosphates of the glycation of human hemoglobin

Abstract

The non‐enzymic glycation of hemoglobin is catalyzed by 3‐phosphoglycerate, 2‐phosphoglycerate and 2‐glycerolphosphate, but not by sodium propionate. Solvent isotope effects were determined (k/k). Catalysis by 3‐phosphoglycerate, 2‐phosphoglycerate and 2‐glycerolphosphate, the observer solvent isotope effect of unity, and flat proton inventory tend to suggest that the proton abstraction step of the Amadori rearrangement by 3‐phosphoglycerate, 2‐phosphoglycerate and 2‐glycerolphosphate is the rate‐determining step in the non‐enzymatic glycation of hemoglobin. The solvent isotope effect of unity, and a flat proton inventory for sodium propionate are indicative that a functional group on the hemoglobin is the proton‐abstracting base in the Amadori rearrangement. Copyright © 2002 John Wiley & Sons, Ltd.

Insights into the Progression of Labile Hb A1cto Stable Hb A1cviaa Mechanistic Assessment of 2,3-Bisphosphoglycerate Facilitation of the Slow Nonenzymatic Glycation Process

“…A more complete depiction of labile Hb A 1 formation has been forwarded by Clark et al [4], Rodnick et al [15] and Park et al [23], which includes the recently-discovered detail that the initial glucose species that binds to Hb A is not ringopened but is rather a cyclic glucopyranose that ring-opens while bound as a necessary precondition before it leads to structure 3, the conjugate acid of the Schiff base that is labile Hb A 1c . Gil et al [24] recognized and highlighted that structure 3 is the initially-formed covalent species when a nucleophilic amino acid residue (e.g. the amine form of the Nterminal Val1 on the two β chains of Hb A) reacts with the electrophilic ring-opened form of glucose (structure 2).…”

“…Lowrey et al [22] suggested and Gil et al [24] demonstrated that the formation of stable Hb A 1c structure 6 from labile Hb A 1c structure 3 is largely (or entirely) irreversible and slow, constituting the rate-determining step of NEG for Hb A in the presence of 2,3-BPG. Smith et al [12], extending from their data, posited that the rate of conversion from the conjugate acid of the Schiff base (labile Hb A 1c , structure 3) to stable Hb A 1c (structure 6, the Amadori product; Figure 1, mechanistic pathway I) increases under the influence of nearby 2,3-BPG.…”

“…Smith et al [12], extending from their data, posited that the rate of conversion from the conjugate acid of the Schiff base (labile Hb A 1c , structure 3) to stable Hb A 1c (structure 6, the Amadori product; Figure 1, mechanistic pathway I) increases under the influence of nearby 2,3-BPG. Gil et al [24], using kinetic isotope effect (KIE) analysis, definitively demonstrated that the mechanistic step that determines the rate of stable Hb A 1c formation in the presence of 2,3-BPG is the abstraction of the C2-proton on structure 3, by a base (Figure 1, mechanistic pathway I, with the abstraction of the proton that is rendered in blue). The KIE method of Gil et al [24] did not, however, enable the identification of the specific base (or bases) involved.…”

“…Gil et al [24], using kinetic isotope effect (KIE) analysis, definitively demonstrated that the mechanistic step that determines the rate of stable Hb A 1c formation in the presence of 2,3-BPG is the abstraction of the C2-proton on structure 3, by a base (Figure 1, mechanistic pathway I, with the abstraction of the proton that is rendered in blue). The KIE method of Gil et al [24] did not, however, enable the identification of the specific base (or bases) involved. Our intent is to discern what the base(s) is/are that deprotonate the C2 proton on labile Hb A 1c structure 3 in the progression towards stable Hb A 1c structure 6 and to determine whether other acid/base and/or nucleophile/electrophile reactions can occur that alter the rate of progression from structures 3 to 6.…”

Effect of phosphate buffer on the kinetics of glycation of proteins

“…In addition, other physiological factors have an influence on the rate of hemoglobin A 1C formation, including oxygen tension and 2,3-diphosphoglycerate, 3-phosphoglycerate and 2-phosphoglycerate levels. [11][12][13][14][15] Structural studies of glycated proteins also have emphasized that the reactivity of a particular amino group is highly dependent on its microenvironment within the protein. 16 The amino groups of a single protein react at different rates.…”