Reactivity of the amino groups of carbonmonoxyhemoglobin S with glyceraldehyde

Metabolite interactions in the bacterial Calvin cycle and implications for flux regulation

Metabolite-level regulation of enzyme activity is important for microbes to cope with environmental shifts. Knowledge of such regulations can also guide strain engineering for biotechnology. Here we apply limited proteolysis-small molecule mapping (LiP-SMap) to identify and compare metabolite-protein interactions in the proteomes of two cyanobacteria and two lithoautotrophic bacteria that fix CO2 using the Calvin cycle. Clustering analysis of the hundreds of detected interactions shows that some metabolites interact in a species-specific manner. We estimate that approximately 35% of interacting metabolites affect enzyme activity in vitro, and the effect is often minor. Using LiP-SMap data as a guide, we find that the Calvin cycle intermediate glyceraldehyde-3-phosphate enhances activity of fructose-1,6/sedoheptulose-1,7-bisphosphatase (F/SBPase) from Synechocystis sp. PCC 6803 and Cupriavidus necator in reducing conditions, suggesting a convergent feed-forward activation of the cycle. In oxidizing conditions, glyceraldehyde-3-phosphate inhibits Synechocystis F/SBPase by promoting enzyme aggregation. In contrast, the glycolytic intermediate glucose-6-phosphate activates F/SBPase from Cupriavidus necator but not F/SBPase from Synechocystis. Thus, metabolite-level regulation of the Calvin cycle is more prevalent than previously appreciated.

A Perspective on Reagent Diversity and Non-covalent Binding of Reactive Carbonyl Species (RCS) and Effector Reagents in Non-enzymatic Glycation (NEG): Mechanistic Considerations and Implications for Future Research

This perspective focuses on illustrating the underappreciated connections between reactive carbonyl species (RCS), initial binding in the nonenzymatic glycation (NEG) process, and nonenzymatic covalent protein modification (here termed NECPM). While glucose is the central species involved in NEG, recent studies indicate that the initially-bound glucose species in the NEG of human hemoglobin (HbA) and human serum albumin (HSA) are non-RCS ring-closed isomers. The ring-opened glucose, an RCS structure that reacts in the NEG process, is most likely generated from previously-bound ring-closed isomers undergoing concerted acid/base reactions while bound to protein. The generation of the glucose RCS can involve concomitantly-bound physiological species (e.g., inorganic phosphate, water, etc.); here termed effector reagents. Extant NEG schemes do not account for these recent findings. In addition, effector reagent reactions with glucose in the serum and erythrocyte cytosol can generate RCS (e.g., glyoxal, glyceraldehyde, etc.). Recent research has shown that these RCS covalently modify proteins in vivo via NECPM mechanisms. A general scheme that reflects both the reagent and mechanistic diversity that can lead to NEG and NECPM is presented here. A perspective that accounts for the relationships between RCS, NEG, and NECPM can facilitate the understanding of site selectivity, may help explain overall glycation rates, and may have implications for the clinical assessment/control of diabetes mellitus. In view of this perspective, concentrations of ribose, fructose, Pi, bicarbonate, counter ions, and the resulting RCS generated within intracellular and extracellular compartments may be of importance and of clinical relevance. Future research is also proposed.

The structural feature surrounding glycated lysine residues in human hemoglobin

Complications derived from diabetes mellitus are caused by nonenzymatic protein glycation at the specific sites. LC/MS/MS was performed for the identification of the tryptic peptides of glycated hemoglobins using glyceraldehyde. After the identification of the glycation or non-glycation site, computer analysis of the structure surrounding the sites was carried out using PDB data (1BZ0). Five glycated lysine residues (Lys-16(α), -56(α), -8(β), -82(β), and -144(β)) and four non-glycated lysine residues (Lys-7(α), -40(α), -99(α), and -132(β)) were identified. The non-glycated lysine residues, Lys-7(α), -40(α), and -132(β), are most likely to form electrostatic interactions with the β carboxyl group of Asp-74(α), C-terminal His-146(β), and Glu-7(β) by virtue of their proximity, which is 2.67-2.91 Å (N-O). Additionally, there are histidine residues within 4.55-7.38 Å (N-N) around eight sites except for Lys-7(α). We conclude that the following factors seem to be necessary for glycation of lysine residues: (i) the apparent absence of aspartate or glutamate residues to inhibit the glycation reaction by forming an electrostatic interaction, (ii) the presence of histidine residues for acid-base catalysis of the Amadori rearrangement, and (iii) the presence of an amino acid residue capable of stabilizing a phosphate during proton transfer.

Erythrocyte-active agents and treatment of sickle cell disease

The sickle hemoglobin (HbS)-containing erythrocyte and its membrane represent a logical target for sickle cell disease therapy. Several antisickling agents which interfere with HbS polymerization have been studied over the last 30 years, but none has overcome the challenge of delivering high concentrations inside the sickle red blood cell without toxicity. The sickle erythrocyte membrane has also been targeted for therapeutic developments. Prevention of sickle cell dehydration by use of specific blockers of ion transport pathways mediating potassium loss from the sickle erythrocyte has been shown to be a feasible strategy in vitro, in vivo in transgenic sickle mice, and in patients. Other approaches have focused on improving the hemorheology of sickle erythrocytes and reducing their abnormal adhesion to endothelial cells. These potential treatments could be used alone or in combination with other approved therapies, such as hydroxyurea.

Restriction in the conformational flexibility of apoproteins in the presence of organic cosolvents: a consequence of the formation of "native-like conformation"

The influence of n-propanol on the overall alpha-helical conformation of beta-globin, apocytochrome C, and the functional domain of streptococcal M49 protein (pepM49) and its consequence on the proteolysis of the respective proteins has been investigated. A significant amount of alpha-helical conformation is induced into these proteins at pH 6.0 and 4 degrees C in the presence of relatively low concentrations of n-propanol. The induction of alpha-helical conformation into the proteins increased as a function of the propanol concentration, the maximum induction occurring around 30% n-propanol. In the case of alpha-globin, the fluorescence of its tryptophyl residues also increased as a function of n-propanol concentration, the midpoint of this transition being around 20% n-propanol. Furthermore, concomitant with the induction of helical conformation into these proteins, the proteolysis of their polypeptide chain by V8 protease also gets restricted. The alpha-helical conformation induced into alpha- and beta-globin by n-propanol decreased as the temperature is raised from 4 to 24 degrees C. In contrast, the alpha-helical conformation of both alpha- and beta-chain (i.e., globin with noncovalently bound heme) did not exhibit such a sensitivity to this change in temperature. However, distinct differences exist between the n-propanol induced "alpha-helical conformation" of globins and the "alpha-helical conformation" of alpha- and beta-chains. A cross-correlation of the n-propanol induced increase in the fluorescence of beta-globin with the corresponding increase in the alpha-helical conformation of the polypeptide chain suggested that the fluorescence increase represents a structural change of the protein that is secondary to the induction of the alpha-helical conformation into the protein (i.e., an integration of the helical conformation induced to the segments of the polypeptide chain to influence the microenvironment of the tryptophyl residues). Presumably, the fluorescence increase is a consequence of the packing of the helical segments of globin to generate a "native-like structure." The induction of alpha-helical conformation into these proteins in the presence of n-propanol and the consequent generation of "native-like conformation" is not unique to n-propanol. Trifluoroethanol, another helix-inducing organic solvent, also behaves in the same fashion as n-propanol. However, in contrast to the proteins described above, n-propanol could neither induce an alpha-helical conformation into performic acid oxidized RNAse-A nor restrict its proteolysis by proteases.(ABSTRACT TRUNCATED AT 400 WORDS)

Aldimine to ketoamine isomerization (Amadori rearrangement) potential at the individual nonenzymic glycation sites of hemoglobin A: preferential inhibition of glycation by nucleophiles at sites of low isomerization potential

The relative roles of the two structural aspects of nonenzymic glycation sites of hemoglobin A, namely the ease with which the amino groups could form the aldimine adducts and the propensity of the microenvironments of the respective aldimines to facilitate the Amadori rearrangement, in dictating the site selectivity of nonenzymic glycation with aldotriose has been investigated. The chemical reactivity of the amino groups of hemoglobin A for in vitro reductive glycation with aldotriose is distinct from that in the nonreductive mode. The reactivity of amino groups of hemoglobin A toward reductive glycation (i.e., propensity for aldimine formation) decreases in the order Val-1(beta), Val-1(alpha), Lys-66(beta), Lys-61(alpha), and Lys-16(alpha). The overall reactivity of hemoglobin A toward nonreductive glycation decreased in the order Lys-16(alpha), Val-1(beta), Lys-66(beta), Lys-82(beta), Lys-61(alpha), and Val-1(alpha). Since the aldimine is the common intermediate for both the reductive and nonreductive modification, the differential selectivity of protein for the two modes of glycation is clearly a reflection of the propensity of the microenvironments of nonenzymic glycation sites to facilitate the isomerization reaction (i.e., Amadori rearrangement). A semiquantitative estimate of this propensity of the microenvironment of the nonenzymic glycation sites has been obtained by comparing the nonreductive (nonenzymic) and reductive modification at individual glycation sites. The microenvironment of Lys-16(alpha) is very efficient in facilitating the rearrangement and the relative efficiency decreases in the order Lys-16(alpha), Lys-82(beta), Lys-66(beta), Lys-61(alpha), Val-1(beta), and Val-1(alpha). The propensity of the microenvironment of Lys-16(alpha) to facilitate the Amadori rearrangement of the aldimine is about three orders of magnitude higher than that of Val-1(alpha) and is about 50 times higher than that of Val-1(beta). The extent of nonenzymic glycation at the individual sites is modulated by various factors, such as the pH, concentration of aldotriose, and the concentration of the protein. The nucleophiles--such as tris, glycine ethyl ester, and amino guanidine--inhibit the glycation by trapping the aldotriose. The nonenzymic glycation inhibitory power of nucleophile is directly related to its propensity to form aldimine. Thus, the extent of inhibition of nonenzymic glycation at a given site by a nucleophile directly reflects the relative role of pKa of the site in dictating the glycation at that site.(ABSTRACT TRUNCATED AT 400 WORDS)

Proteosynthetic activity of immobilized Staphylococcus aureus V8 protease: application in the semisynthesis of molecular variants of alpha-globin

The proteosynthetic activity of Staphylococcus aureus V8 protease (endoproteinase Glu-C) immobilized onto cross-linked agarose beads by reductive alkylation procedure has been investigated. The overall substrate specificity of the enzyme, as judged by peptide mapping of performic acid oxidized RNase A, as well as the high propensity of the protease to slice selectively the alpha-chain of hemoglobin (Hb) A at the Glu(30)-Arg(31) peptide bond at pH 4.0 and 37 degrees C was essentially unperturbed by the immobilization process. This high susceptibility of Glu(30) of the alpha-chain for proteolysis appears to be a consequence of the conformational aspects of the polypeptide in this region. The proteolysis of two mutant forms of alpha-chain, namely, those of Hb I (K16E) and Hb Sealy (D47H) by immobilized V8 protease at the Glu(30)-Arg(31) peptide bond proceeds with the same selectivity. The immobilized protease also retained the proteosynthetic activity, i.e., the ability to ligate the unprotected alpha-globin fragments at the Glu(30)-Arg(31) peptide bond in the presence of 30% 1-propanol. The use of the insoluble enzyme simplifies the procedures for the construction of new semisynthetic, molecular variants of alpha-globin. The general applicability of the immobilized enzyme for protein semisynthesis has been demonstrated by the construction of a doubly mutated alpha-globin. The complementary fragments from two natural mutant forms of alpha-globin, viz., alpha 1-30 (K16E) from Hb I and alpha 31-141 (D47H) from Hb Sealy, are readily ligated to form the double mutant alpha 1-141 (K16E;D47H).

Basic carboxyl groups of hemoglobin S: influence of oxy-deoxy conformation on the chemical reactivity of Glu-43(beta)

The gamma-carboxyl groups of Glu-43(beta) and Glu-22(beta) of hemoglobin-S (HbS), two intermolecular contact residues of deoxy protein, are activated by carbodiimide at pH 6.0. The selectivity of the modification by the two nucleophiles, glycine ethyl ester (GEE) and glucosamine, is distinct. Influence of N-hydroxysulfosuccinimide, a reagent that rescues carbodiimide-activated carboxyl (O-acyl isourea) as sulfo-NHS ester, on the overall selectivity and efficiency of the coupling of Glu-22(beta) and Glu-43(beta) with nucleophiles has been investigated. Sulfo-NHS increases the extent of coupling of nucleophiles to HbS. The rescuing efficiency of sulfo-NHS(increase in modification) with GEE and galactosamine as nucleophiles is 2.0 and 2.8, respectively. In the presence of sulfo-NHS, the extent of modification of a carboxyl group is a direct reflection of the extent to which it is activated (i.e., the protonation state of the carboxyl group). The modification reaction exhibits very high selectivity for Glu-43(beta) with GEE and galactosamine (GA) in the presence of sulfo-NHS. From the studies of the kinetics of amidation of oxy-HbS at its Glu-43(beta) (i.e., chemical reactivity) as a function of the pH in the region of 5.5-7.5, the apparent pKa of its gamma-carboxyl group has been calculated to be 6.35. Deoxygenation of HbS, nearly doubles the chemical reactivity of Glu-43(beta) of HbS at pH 7.0. It is suggested that the increased hydrophobicity of the microenvironment of Glu-43(beta), which occurs on deoxygenation of the protein, is reflected as the increased chemical reactivity of the gamma-carboxyl group and could be one of the crucial preludes to the polymerization process.

Sequence-dependent reactivity of model peptides with glyceraldehyde

Glyceraldehyde reacted faster with tripeptides than with dipeptides. The pH profiles of the reactions with tripeptides displayed optima in the range of 8.5-10.0, approximately 1-2 pH units higher than found with dipeptides. The second amino acid residue influences not only the rate of reaction but also the extent of formation of the product of the Amadori rearrangement, the ketoamine. The presence of histidine as the second amino acid residue of either di- or tri-peptides greatly accelerated the rate of reaction perhaps by facilitating the rearrangement. Conventional amino acid analysis and liquid chromatography procedures have been used to detect intermediates and the ketoamine product. 1H-N.m.r. analysis of the reduced adducts was consistent with the assigned structures.

Some factors that influence the nonenzymatic glycation of peptides and polypeptides by glyceraldehyde

The rate of reaction of glyceraldehyde with a series of peptides was found to be dependent on their amino acid composition, sequence, and chain length. The presence of a histidine near the NH2-terminal increased the rate of glycation, whereas the presence of a carboxyl group near the reaction site led to a decrease in reaction rate. In general, tripeptides reacted faster than dipeptides, and dipeptides reacted faster than amino acids. Sodium phosphate and 2,3-diphosphoglycerate enhanced the rate of reaction of glyceraldehyde with all the dipeptides tested. Sodium chloride inhibited the reaction in phosphate buffer, but not in HEPES buffer. The NH2-terminal heptapeptide from the beta-chain of human hemoglobin A (HbA), where histidine is the second residue, reacted with glyceraldehyde faster than the NH2-terminal hexapeptide from the alpha-chain. The glycation of tetrameric human Hb by glyceraldehyde was found to be dependent on the ligation state of the protein since deoxy-HbA reacted about 50% more with glyceraldehyde than did liganded HbA. The enhanced glycation of deoxy HbA was mainly attributable to the more extensive reaction at the NH2-terminal of the beta-chain. The presence of a histidine adjacent to the NH2-terminal at this site may facilitate the Amadori rearrangement. The glycation of horse Hb in which the second residue is glutamine was not increased under anaerobic conditions.

Selective amidation of carboxyl groups of the intermolecular contact regions of hemoglobin S: structural aspects

Carboxyl groups of HbS are readily activated by water-soluble carbodiimide at pH 6.0 and room temperature. These o-acylurea intermediates (activated carboxyl) are accessible for nucleophilic attack by amines. With glycine ethyl ester, the amidation is very selective for the gamma-carboxyl of Glu-43(beta) and more than 65% of the glycine ethyl ester incorporated is on this carboxyl group. In contrast, glucosamine derivatizes the gamma-carboxyl group of Glu-22(beta) as well as that of Glu-43(beta) to nearly the same degree. However, the total amidation of HbS by glucosamine is lower than that with glycine ethyl ester. The differential selectivity of the two amines is apparently related to the differences in the microenvironment of the gamma-carboxyl groups of Glu-22(beta) and Glu-43(beta), which either facilitates or refracts the aminolysis of the activated carboxyl with the two amines to different degrees. The carboxyl groups of isolated beta-chain exhibit a higher reactivity for amidation with glycine ethyl ester than does the tetramer. The carboxyl groups of Glu-22(beta) and Glu-43(beta) and that of Asp-47(beta) are all activated by carbodiimide suggesting that the higher pKa of these carboxyl groups (facilitating the activation) is a property of tertiary interaction of the polypeptide chain. The interaction of the beta-chain with alpha-chain, i.e., generation of the quaternary interactions, reduces overall reactivity of the carboxyl groups of the protein. The higher selectivity of hemoglobin S for amidation at Glu-43(beta) with glycine ethyl ester compared with that of isolated beta-chain appears to be primarily a consequence of decreased amidation at sites other than at Glu-43(beta).

Hemoglobin-based blood substitutes: characterization of five pyridoxal 5'-phosphate derivatives of hemoglobin

Six fractions (I-VI) of pyridoxal 5'-phosphate (PLP) hemoglobin (Hb), prepared by the method of De Venuto and Zegna [J. Surg. Res., 34 (1983) 205] have been isolated and purified by anion-exchange high-performance liquid chromatography (HPLC). Total phosphate analyses indicate that I is HbA, II and III are double-labelled, IV and V are tetra-labelled and VI contains 6 mol of phosphorus per mol of hemoglobin. The purified components have been resolved into their alpha and beta chains by preparative reversed-phase HPLC using a macroporous C4 support. Phosphate analyses indicate that the beta chains of II, III and IV each contain one phosphate per chain while the beta chains of V and VI each contain two phosphates. The alpha chains of IV and VI were found to be monophosphate-labelled. Reversed phase HPLC analysis of the tryptic peptides of the beta chains indicates that the label is bound exclusively to the 1-valine residue in II, III and IV while both the 1-valine and the 82-lysine are labelled in V and VI. Similarly, modification of the 1-valine residue of the alpha chains of IV and VI was detected. Components II and III have the same molecular formula. Evidence is presented which shows that they are interconvertible and that they correspond to the PLP2-Hb species and component V is Benesch's PLP4-Hb [J. Biol. Chem., 257 (1983) 1320 and references cited therein]. Component IV is III with one additional PLP per alpha chain and similarly VI is V with monolabelled alpha chains.(ABSTRACT TRUNCATED AT 250 WORDS)

Permissible discontinuity region of the alpha-chain of hemoglobin: noncovalent interaction of heme and the complementary fragments alpha 1-30 and alpha 31-141

Generation of a fragment-complementing system of the alpha-chain on limited proteolysis with Staphylococcus aureus V8 protease has been investigated. Digestion of the alpha-chain (0.4 mM) of hemoglobin with V8 protease in phosphate buffer at pH 6.0 and 37 degrees C is limited to the peptide bonds of Glu-23, Glu-27, Glu-30, and Asp-47. Gel filtration of a V8 protease digest of the alpha-chain on a Sephadex G-50 column did not release any heme to the low molecular weight region, though some peptides were released from the protein. The filtration studies revealed the presence of two heme-containing components in the digest, the major one eluting at the alpha-chain position and the minor one eluting slightly ahead of the alpha-chain position. Reversed-phase high-performance liquid chromatography and amino-terminal sequence analysis demonstrated that the component eluting at the alpha-chain position contains species generated by the noncovalent interactions of heme and the complementary fragments alpha 1-30 and alpha 31-141. In dilute solutions (0.04 mM) the V8 protease digestion occurred exclusively on the carboxyl side of Glu-30(alpha). This high selectivity was also observed at pH 4.0 and pH 7.8. The visible spectra and the ultraviolet circular dichroic spectra of the digest reflect the native-like structure of the noncovalent fragment system. The dissociation constant of alpha 1-30 appears to be in the range of 10(-8) M. In tetrameric hemoglobin A the peptide bond of Glu-30-Arg-31 of the alpha-chain is not accessible to V8 protease digestion.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the Amadori rearrangement in a model system: chromatographic isolation of intermediates and product

The pH profile of the reaction of glyceraldehyde with either valylhistidine or alanylhistidine exhibits an optimum near pH 6.5. One of the intermediates in the reaction, the Schiff base (aldimine), can be readily detected on an amino acid analyzer. The product of the reaction, the ketoamine formed after Amadori rearrangement of the aldimine, has been isolated by chromatography on Dowex 50. Its structure has been established by elemental analysis, amino acid analysis, and the relative amounts of carbonyl and histidine moieties. These chromatographic systems should facilitate studies on the mechanism of this reaction as it relates to peptides and proteins.

Synthetic potential of Staphylococcus aureus V8-protease: an approach toward semisynthesis of covalent analogs of alpha-chain of hemoglobin S

Enzyme-catalyzed reformation of peptide bonds in the noncovalent fragment systems of proteins has been emerging as a convenient procedure for the semisynthesis of covalent analogs of the respective proteins. Limited proteolysis of the alpha-chain of hemoglobin S with Staphylococcus aureus V8-protease converts the chain into a fragment-complementing system by hydrolyzing the peptide bond Glu(30)-Arg(31) of the chain. Therefore, it is conceivable that semisynthesis of covalent analogs of alpha-chain could be achieved if conditions for the V8-protease catalyzed formation of peptide bonds could be established. The synthetic potential of V8-protease has been now investigated by incubating V8-protease-derived fragments of alpha-chain, namely alpha 1-30 and alpha 31-47 with the enzyme at pH 6.0 in the presence of n-propanol as the organic cosolvent. RP high performance liquid chromatography analysis showed that a new chromatographically distinct component is generated on incubation, and this has been identified as alpha 1-47 by amino acid analysis, redigestion with V8-protease (in the absence of n-propanol), and tryptic peptide mapping. Optimal conditions for the synthesis of alpha 1-47 is at pH 6.0, 4 degrees C, and 24 hr of incubation with 25% n-propanol as organic cosolvent. This stereospecific condensation of the fragments proceeded to a high level of about 50% in 24 hr. Further incubation up to 72 hr did not increase the yield of alpha 1-47, suggesting that an equilibration of synthesis and hydrolysis reactions has been attained. The demonstration of the synthetic potential of V8-protease and the fact that alpha 1-30 and alpha 31-141 interact to form a native-like complex, opens up an approach for the semisynthesis of covalent analogs of alpha-chain of hemoglobin S.

Application of reductive dihydroxypropylation of amino groups of proteins in primary structural studies: identification of phenylthiohydantoin derivative of epsilon-dihydroxypropyl-lysine residues by high-performance liquid chromatography

The general utility of reductive alkylation of amino groups of proteins with glyceraldehyde (2,3-dihydroxypropionaldehyde) in the presence of sodium cyanoborohydride, i.e. dihydroxypropylation, as an aid in generating arginine peptides of proteins by tryptic digestion has been investigated. The dihydroxypropylation of the amino groups of ribonuclease A and the streptococcal Pep M5 protein proceeds predominantly to the stage of monoalkylation. The derivatized lysine namely, epsilon-dihydroxypropyl-lysine is stable to acid hydrolysis, and is eluted slightly ahead of histidine in the amino acid analyzer. The peptide bonds of epsilon-dihydroxypropyl-lysine residues are resistant to tryptic digestion. The arginine peptides of dihydroxypropylated ribonuclease A, and dihydroxypropylated streptococcal Pep M5 protein have been isolated by reversed-phase high-performance liquid chromatography (HPLC) of the tryptic digest of the derivatized proteins. The phenylthiohydantoin (PTH) derivative of epsilon-dihydroxypropyl-lysine has been prepared. It is eluted at a position intermediate to that of the PTH derivatives of proline and tryptophan in reversed-phase HPLC on DuPont Zorbax ODS columns. Thus the PTH-epsilon-dihydroxypropyl-lysine could be identified during the sequence studies of the dihydroxypropylated peptides. The presence of dihydroxypropyl groups on the epsilon-amino groups of lysine residues in the dihydroxypropylated peptides does not interfere with the Edman degradation studies. The ease of the dihydroxypropylation reaction, the resistance of the peptide bonds of epsilon-dihydroxypropyl-lysine residues to trypsin, and the identification of the PTH derivative of epsilon-dihydroxypropyl-lysine residues by reversed-phase HPLC makes the dihydroxypropylation procedure a valuable addition to the arsenal of procedures for limiting the tryptic digestion to the arginine residues of proteins and peptides.

The effect of glyceraldehyde on red cells. Haemoglobin status, oxidative metabolism and glycolysis

Glyceraldehyde induces changes in the flux of glucose oxidised through the hexose monophosphate pathway, the concentrations of intermediates in the Embden-Meyerhoff pathway, the oxidative status of haemoglobin and levels of reduced and oxidised pyridine nucleotides and glutathione in red cells. Glyceraldehyde autoxidises in the cellular incubations, consuming oxygen and producing glyoxalase I- and II-reactive materials. Major fates of glyceraldehyde in red cells appear to be: (i) adduct formation with reduced glutathione and cellular protein; (ii) autoxidation and reaction with oxyhaemoglobin and pyridine nucleotides, and (iii) phosphorylation of D-glyceraldehyde and entry into the glycolytic pathway as glyceraldehyde 3-phosphate. The production of glycerol from glyceraldehyde by red cell L-hexonate dehydrogenase appears not to be a major reaction of glyceraldehyde in red cells. These results indicate that high concentrations of glyceraldehyde (1-50 mM) may induce oxidative stress in red cells by virtue of the spontaneous autoxidation of glyceraldehyde, forming hydrogen peroxide and alpha-ketoaldehydes (glyoxalase substrates). The implications of glyceraldehyde-induced oxidative stress for the in vitro anti-sickling effect of DL-glyceraldehyde and for the polyol pathway metabolism of glyceraldehyde are discussed.

Inhibition of deoxyhemoglobin S polymerization by glyceraldehyde

Glyceraldehyde reacts with hemoglobin S in the intact erythrocyte to reduce the degree of polymerization, thereby inhibiting sickling of the erythrocyte. Only five of the 24 amino groups per alpha beta dimer react with glyceraldehyde; the adducts are present as ketoamine structures, formed by Amadori rearrangement of the initial Schiff base adducts on the protein. The reactive amino groups are the epsilon-amino group of Lys-16 of the alpha-chain, and the alpha-amino group of Val-1 as well as the epsilon-amino groups Lys-82, Lys-59, and Lys-120 of the beta-chain. Hybrid tetramers were prepared with the modification only on Lys-16 of the alpha-chain or on the reactive lysine residues of the beta-chain. The former derivative gels at a much higher hemoglobin concentration (23 g/dl) than either the latter derivative (16 g/dl) or unmodified deoxyhemoglobin S (15 g/dl). Thus, the modification at Lys-16 of the alpha-chain is a major factor in the inhibition of sickling by glyceraldehyde.

Influence of trifluoroacetic acid on retention times of histidine-containing tryptic peptides in reverse phase HPLC

The tryptic peptides of the aminoethylated alpha- and beta-chain of hemoglobin have been separated on a Partisil-10 ODS-2 column with a linear gradient of acetonitrile containing 0.1% trifluoroacetic acid. The elution profile of the tryptic peptides of the chains obtained with this acetonitrile trifluoroacetate system has been compared with that obtained using phosphoric acid as the ion-pairing reagent. This comparison demonstrated that trifluoroacetate influences the retention times of the histidine-containing tryptic peptides much more than it affects those peptides that do not contain histidine residues. This behavior has been rationalized on the basis of ion-pairing of trifluoroacetate with the histidine residues of the tryptic peptides.