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Biomedical subjects

A S Acharya

Publications and source records attributed to A S Acharya.

At least 37 records · Page 2Linked to original sources
PubMed1999

Bacillus sphaericus interferes with the development of Brugia malayi in Aedes aegypti.

Aedes aegypti (black-eyed Liverpool strain) were exposed to a sublethal dose (LD25) of Bacillus sphaericus and were fed to Mastomys coucha infected with Brugia malayi. The development of the filarial parasite was found to be arrested mostly at the second larval stage. The infection (P < 0.05), infectivity rates (P < 0.001) and L3 load (P < 0.001) were found to be reduced significantly in the treated group.

Aedes↗
PubMed1998

Chemistry of the "molecular trap" of protease-catalyzed splicing reaction of complementary segments of alpha-subunit of hemoglobin A.

The complementary fragments of human Hb alpha, alpha1-30, and alpha31-141 are spliced together by V8 protease in the presence of 30% n-propanol to generate the full-length molecule (Hb alpha-semisynthetic reaction). Unlike the other protease-catalyzed protein/peptide splicing reactions of fragment complementing systems, the enzymic condensation of nonassociating segments of Hb alpha is facilitated by the organic cosolvent induced alpha-helical conformation of product acting as the "molecular trap" of the splicing reaction. The segments alpha24-30 and alpha31-40 are the shortest complementary segments that can be spliced by V8 protease. In the present study, the chemistry of the contiguous segment (product) alpha24-40 has been manipulated by engineering the amino acid replacements to the positions alpha27 and alpha31 to delineate the structural basis of the molecular trap. The location of Glu27 and Arg31 residues in the contiguous segment alpha24-40 (as well as in other larger segments) is ideal to generate (i, i + 4) side-chain carboxylate-guanidino interaction in its alpha-helical conformation. The amino acid residue replacement studies have confirmed that the side chains at alpha27 and alpha31 facilitate the semisynthetic reaction. The relative influence of the substitute at these sites on the splicing reaction depends on the chemical nature of the side chain and the location. The gamma-carboxylate guanidino side-chain interaction appears to contribute up to a maximum of 85% of the thermodynamic stability of the molecular trap. The studies also demonstrate that the thermodynamic stability of the molecular trap is determined by two interdependent conformational aspects of the peptide. One is an amino acid-sequence-specific event that facilitates the induction of an alpha-helical conformation to the contiguous segment in the presence of organic cosolvent that imparts some amount of protease resistance to Glu30-Arg31 peptide bond. The second structural aspect is a site-specific event, an i, i + 4 side-chain interaction in the alpha-helical conformation of the peptide which imparts an additional thermodynamic stability to the molecular trap. The results suggest that conformationally driven "molecular traps" of protease-mediated ligation reactions of peptides could be designed into products to facilitate the modular assembly of peptides/proteins.

1-Propanol↗
PubMed1998

Correct assembly of human normal adult hemoglobin when expressed in transgenic swine: chemical, conformational and functional equivalence with the human-derived protein.

Structural and functional investigations of recombinant human hemoglobin A (HbA) isolated from the erythrocytes of transgenic swine coexpressing human alpha- and beta-globins have been carried out to authenticate its correct expression, post-translational processing and assembly. The HbA expressed in transgenic swine (TgHbA) is indistinguishable from the human-derived HbA in terms of its isoelectric pH, mass and elution pattern on a Mono S column. The chemical identity of the alpha- and beta-globin chains of TgHbA with the corresponding chains from human-derived HbA has been established by tryptic peptide mapping and amino acid sequencing. The proton NMR spectra of TgHbA have demonstrated that the conformational aspects of the protein around the heme pocket are indistinguishable from those of the control sample of HbA. The equivalence of the hydrogen bond pattern of TgHbA (in particular the inter-subunit surfaces) with that of authentic HbA has also been established by NMR studies. Consistent with these structural and conformational analyses, the TgHbA also exhibits complete functional equivalence with the human-derived HbA with respect to oxygen affinity, cooperativity, Bohr effect and allostery. Hence the studies presented here demonstrate that the transgenic swine system correctly transcribes the alpha- and beta-globin transgenes, translates the respective alpha- and beta-globin mRNA to generate the corresponding globin chains, carries out the correct cotranslational processing of the translated globin chains, inserts the heme into the globin chains in the same orientation as in the human-derived HbA and assembles the alpha- and beta-subunits into a functionally cooperative tetramer that exhibits a response to allosteric effectors identical with that of human-derived HbA. Thus, in the transgenic swine system, in vitro chemical manipulation steps such as those needed in the Escherichia coli and the yeast systems, to convert the rHbA expressed in these systems into forms functionally identical with that of the human-derived protein, are not needed. An additional advantage of the transgenic swine system is the stability of the transgenes over many generations. Hence the transgenic swine could serve as an excellent system for the production of human HbA (or its variants) for structure-function studies and for therapeutic applications.

Adult↗
PubMed1998

Transmission dynamics of filariasis in Khurdha district of Orissa, India.

A three year longitudinal study was carried out to quantify the different parameters of filarial transmission in an endemic area of Orissa State, India. Parasitological surveys revealed mean microfilaria rate, microfilaria density and median microfilaria density (MFD-50) to be 9.41, 19.23 and 7.33, respectively. The per man hour density of the vector, Culex quinquefasciatus varied from 24.2 to 66.0 with a peak in January. Infection rate varied from 0.9 to 27.5%, while infectivity rate ranged between 0.0 and 15.2%. Infectivity rate showed high correlation with microfilaria rate and per man hour density of adult mosquito. The highest numbers of first stage larvae (L1), second stage larvae (L2) and third stage larvae (L3) per mosquito were found to be 25, 22 and 11, respectively. Average L3 load per infective mosquito ranged from 1.0 to 7.2. L3 load showed high correlation with microfilaria rate (r = 0.845, p < 0.01) while no correlation was seen with microfilaria density.

Animals↗
PubMed1997

Inhibition of sickle beta-chain (betaS)-dependent polymerization by nonhuman alpha-chains. A superinhibitory mouse-horse chimeric alpha-chain.

Horse alpha-chain inhibits sickle beta-chain-dependent polymerization; however, its inhibitory potential is not as high as that of mouse alpha-chain. Horse alpha-(1-30) and alpha-(31-141) segments make, respectively, minor and major contributions to the inhibitory potential of horse alpha-chain. The sum of the inhibitory potential of the two segments does not account for the inhibitory potential of the full-length horse alpha-chain. Although the polymerization inhibitory potential of horse alpha-chain is lower than mouse alpha-chain, the inhibitory potential of horse alpha-(31-141) is comparable to that of mouse alpha-(31-141). When mouse alpha-(1-30) is stitched to horse alpha-(31-141), the product is a chimeric alpha-chain with an inhibitory potential greater than mouse alpha-chain. In contrast, the stitching of horse alpha-(1-30) with mouse alpha-(31-141) had no additional inhibitory potential. Molecular modeling studies of HbS containing the mouse-horse chimeric alpha-chain indicate altered side-chain interactions at the alpha1beta1 interface when compared with HbS. In addition, the AB/GH corner perturbations facilitate a different stereochemistry for the interaction of the epsilon-amino group of Lys-16(alpha) with the beta-carboxyl group of Asp-116(alpha), resulting in a decrease in the accessibility of the side chain of Lys-16(alpha) to the solvent. Based on molecular modeling, we speculate that these perturbations by themselves, or in synergy with the altered conformational aspects of the alpha1beta1 interactions, represent the molecular basis of the superinhibitory potential of the mouse-horse chimeric alpha-chains.

Animals↗
PubMed1997

Probing the hemoglobin central cavity by direct quantification of effector binding using fluorescence lifetime methods.

Time-resolved fluorescence methods have been used to show that 8-hydroxy-1,3,6-pyrenetrisulfonate (HPT), a fluorescent analog of 2,3-diphosphoglycerate, binds to the central cavity of carboxyhemoglobin A (HbACO) at pH 6.35. A direct quantitative approach, based on the distinctive free and bound HPT fluorescent lifetimes of 5.6 ns and approximately 27 ps, respectively, was developed to measure the binding affinity of this probe. HPT binds to a single site and is displaced by inositol hexaphosphate at a 1:1 mol ratio, indicating that binding occurs at the 2,3-diphosphoglycerate site in the central cavity. Furthermore, the results imply that low pH HbACO exists as an altered R state and not an equilibrium mixture of R and T states. The probe was also used to monitor competitive effector binding and to compare the affinity of the binding site in several cross-bridged HbA derivatives.

Adult↗
PubMed1996

Chimeric hemoglobins--hybrids of human and swine hemoglobin: assembly and stability of interspecies hybrids.

Transgenic swine expressing human HbA contained only one of two types of the anticipated interspecies hybrids, namely H alpha 2 P beta 2 (H = human, P = swine). In an attempt to establish whether the absence of the swine alpha and human beta (P alpha 2 H beta 2) hybrid in vivo is a reflection of the lack of complementarity between the interspecies chains to generate appropriate interfaces, we have undertaken the in vitro assembly of swine alpha and human beta chimeric tetramer. In contrast to the in vivo transgenic swine system, in vitro the hybrid of swine alpha human beta chain is assembled readily and the hybrid exhibits normal cooperative oxygen binding. Both the swine alpha human beta and the human alpha swine beta interspecies hybrids are stable around neutral pH and do not segregate into parent tetramers even when mixed together. On the other hand, nearly complete exchange of P alpha chain of P alpha 2 H beta 2 hybrid occurs in the presence of H alpha chain at pH 6.0 and room temperature, resulting in the formation of HbA. However, very little of such an exchange reaction takes place at pH 7.0. These results suggest that the thermodynamic stability of P alpha 2 H beta 2 hybrid is lower compared to that of HbA. In contrast, P beta chain of H alpha 2 P beta 2 hybrid is refractory to exchange with H beta chain at pH 7.0 as well as at pH 6.0, suggesting that the stability of H alpha 2 P beta 2 is higher compared to that of HbA (H alpha 2 H beta 2). The swine alpha human beta chimeric Hb undergoes subunit exchange reaction with human alpha-chain in the presence of 0.9 M MgCl2, at pH 7.0. This demonstrates the lower thermodynamic stability of the intradimeric interactions of the heterodimer even at neutral pH. A synergistic coupling of the intra- and interdimeric interactions of the swine alpha and human beta chain heterodimer is essential for the thermodynamic stability of the chimeric Hb under the physiological conditions. Accordingly, we speculate that the lower thermodynamic stability of P alpha H beta heterodimer (compared to the homodimers H alpha H beta and P alpha P beta) facilitates its segregation into the homodimers by subunit exchange reaction involving either H alpha or P beta. This molecular aspect by itself or possibly along with other cellular aspects of the swine system results in the absence of P alpha 2 H beta 2 hybrid in transgenic swine expressing HbA.

2,3-Diphosphoglycerate↗
PubMed1995

Polymerization of hemoglobin S. Quinary interactions of Glu-43(beta).

Hemoglobin S (HbS) Hoshida and three substituted forms of HbS Hoshida (the substituents being on the amide nitrogen of Gln-43(beta) have been prepared by the amidation of Glu-43(beta) of HbS with ammonia, methylamine, glycine ethyl ester, and galactosamine. The O2 affinity of HbS is increased slightly on amidation of Glu-43(beta). All the four amidated derivatives exhibited nearly the same oxygen affinity. On the other hand, the influence of amidation on the solubility exhibits some sensitivity to the chemical nature of the substituent on the Gln-43(beta). The solubility of HbS Hoshida (a case with no substitution on Gln-43(beta), and the methyl-substituted derivatives are about 33 and 36% higher than that of HbS. The solubility of the HbS modified with the glycine ethyl ester or galactosamine is increased to 41 and 47%, respectively. The first derivative UV spectra of HbS Hoshida and its methyl derivative reflect very little perturbations in their alpha 1 beta 2 interface as compared with that of HbS, whereas the amidated derivatives with larger substituents on Gln-43(beta) reflected noticeable difference. Thus, the increase in the solubility and the oxygen affinity of HbS on the amidation of Glu-43(beta) is primarily a consequence of the loss of the negative charge at 43(beta), a residue proximal to the alpha 1 beta 2 interface. The copolymerization studies of amidated HbS with HbA, and HbS with amidated HbA demonstrate that cis Glu-43(beta) is the "active" residue. This assignment is discrepant with the earlier implication of a trans configuration for this residue in the polymer (Edelstein, S. J. (1981) J. Mol. Biol. 150, 557-575). However, it is consistent with the solution studies of Nagel et al. (Nagel, R. L., Bookchin, R. M., Johnson, J., Labie, D., Wajcman, H.., Isaac-Sodeye, W. A., Honig, G. R., Schiliro, G., Crookstan, J. H., and Matsutomo, K. (1979) Proc. Nat. Acad. Sci. U.S.A. 76, 670-672) and McCurdy et al. (McCurdy, P. R., Lorkin, P. A., Casey, R., Lehmann, H., Uddin, D. E., and Dickson, L. G. (1974) Am. J. Med. 57, 665-760).

Adult↗
PubMed1995

Symmetric interspecies hybrids of mouse and human hemoglobin: molecular basis of their abnormal oxygen affinity.

Interspecies hybrids of HbA and Hb from mouse C57BL/10 [alpha 2M beta 2H and alpha 2H beta 2M (H = human, M = mouse)], representing 19 and 27 sequence differences per alpha beta dimers (as compared with human alpha beta dimer) have been generated in vitro. The efficiency of the assembly of the interspecies hybrids by the alloplex intermediate pathway is about twofold higher than the low-pH-mediated subunit approach. The interspecies hybrids exhibit a cooperative O2 binding. The intrinsic O2 affinity of mouse Hb is slightly lower than HbA, while the 2,3-diphosphoglycerate (DPG) effect is comparable. Interestingly, the interspecies hybrid alpha 2M beta 2H has high O2 affinity (compared to either human or mouse Hb), while the interspecies hybrid alpha 2H beta 2M exhibits a very low O2 affinity. These results suggest that the mouse beta chain generates a tetramer with very low oxygen affinity. However, the complementarity of the mouse alpha and beta chains generates a set of unique interactions that compensate for the low-oxygen-affinity propensity of the mouse beta chain. DPG binds the tetramer in the central cavity formed by the two beta subunits, hence the DPG effects on the interspecies hybrids should be as in the parent molecule. However, the results of the present study demonstrate that the DPG binding pocket is influenced by the nature of the alpha chain present in the tetramer. The mouse alpha chain reduces considerably the DPG right shift of the O2 affinity of the human beta-chain containing hybrid.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1995

Intramolecular cross-linking of oxy hemoglobin by bis sulfosuccinimidyl suberate and sebacate: generation of cross-linked hemoglobin with reduced oxygen affinity.

The sulfosuccinimidyl esters of suberic and sebacic acids readily introduce intramolecular crosslinks into oxy HbA at pH 7.4, the relative efficiency of crosslinking by the suberate ester being slightly higher than that of sebacate. Nearly quantitative intramolecular crosslinking of HbA (0.5 mM) is achieved at pH 7.4 and 4 degrees C by using 5 and 10 fold molar excess of the suberic and sebacic acid, respectively. In contrast to the facile crosslinking reaction seen with the bis sulfosuccinimidyl sebacate, bis sulfosuccinimidyl sebacate and bis (3:5 dibromo salicyl) sebacate did not introduce any crosslinking into HbA despite the fact that the 'crosslinking arm' of the two bifunctional reagents is the same. The discrepant reactivity of the two reagents demonstrates the 'steering' influence of the negative charge of the leaving group of the reagent, namely sulfo succinimidyl moiety to specific domains of HbA rich in positively charged groups. A second advantage is also anticipated in the use of the sulfosuccinimidyl esters of aliphatic dicarboxylic acids. We speculate that the intermediate in the crosslinking reaction mimics the structural aspects of the low oxygen affinity 'psuedo crosslinked Hb'. Conversion of the low oxygen affinity 'psuedocrosslinked Hb' into crosslinked Hb by the formation of the second isopeptide bond may lead to the 'freezing in' of the elements of low oxygen affinity structure. Consistent with this speculation, the suberate crosslinked Hb indeed exhibited low oxygen affinity even though the crosslinking reaction was carried out in the oxy state.(ABSTRACT TRUNCATED AT 250 WORDS)

Cross-Linking Reagents↗
PubMed1994

Influence of the chemical nature of side chain at beta 108 of hemoglobin A on the modulation of the oxygen affinity by chloride ions. Low oxygen affinity variants of human hemoglobin expressed in transgenic pigs: hemoglobins Presbyterian and Yoshizuka.

Hemoglobin A (HbA) and two low oxygen affinity variants of HbA, HbPresbyterian and HbYoshizuka, were produced in transgenic pigs and purified to homogeneity by ion-exchange chromatography. These two variants contain either lysine (HbPresbyterian) or aspartic acid (HbYoshizuka) instead of the normal asparagine residue at position beta 108 in HbA. Transgenic pigs expressed these variants at a level up to 11% and were healthy. Both HbPresbyterian and HbYoshizuka exhibited low O2 affinity (P50 of 21.2 and 18.9, respectively, compared with control HbA value of 11.8 in 0.1 M NaCl, pH 7.5) and retained normal cooperativity with Hill coefficients of 2.9 and 2.5, respectively. HbPresbyterian exhibited Bohr effect comparable with HbA. In contrast, HbYoshizuka had a diminished response to changes in pH. Thus the structural basis of reduced O2 affinity of these variants appears to be distinct: the consequence of mutation at beta 108 is a function of the chemical nature of the side chain. This is further confirmed by the sensitivity of the O2 affinity of the variants to the presence of Cl-. The O2 affinity of HbYoshizuka is insensitive to changes in Cl- concentration, whereas the O2 affinity of HbPresbyterian exhibited a pronounced and dramatic chloride effect. In fact, P50 of HbPresbyterian was identical to that of HbA at very low Cl- concentrations, and the P50 increased to >40 at 0.5 M Cl-. The chloride effect was completely abolished when HbPresbyterian was stabilized at the 2,3-diphosphoglycerate pocket by interdimeric cross-linking. Molecular modeling studies demonstrate that in HbPresbyterian, Cl- can bridge the epsilon-amino group of Lys beta 108 with either the guanidino group of Arg beta 104 or the epsilon-amino group of Lys alpha 99, resulting in the stabilization of the "T" structure. The utility of these low O2 affinity hemoglobins as cell-free oxygen carriers is discussed.

Allosteric Regulation↗
PubMed1994

Electrostatic modification at the amino termini of hemoglobin A.

The structural perturbations of the amino-terminal domains of hemoglobin A resulting from the carbamino adduct formation (a reversible in vivo electrostatic modification reaction) at Val-1(alpha) and Val-1(beta) is expected to be mimicked in the derivatives of HbA reductively alkylated at its alpha-amino terminus with aldehydes containing a negatively charged functional group at their distal end (double-headed reagents). Derivatives of HbA with galacturonic acid linked through alkylamino linkage either to Val-1(alpha) or Val-1(beta) (disubstituted derivatives) as well as to both Val-1(alpha) and Val-1(beta) (tetrasubstituted derivative) have been now prepared. All the three derivatives exhibit normal cooperativity but reduced O2 affinities. The functional consequence of the modification of HbA at its amino termini with D-galacuronic acid has been compared with that of the carboxymethylation of HbA at the same sites. This comparative study suggests that the stereochemistry of the carboxylate ion introduced into beta-cleft of Hb dictates the level of reduction in the O2 affinity of the molecule seen on derivatization. However such a unique stereochemistry of the carboxylate ion of the reagent does not appear to be crucial to lower oxygen affinity when the modification is at the amino terminus of the alpha-chain. The molecular modeling studies demonstrate that the carboxylate ion of the carbamino adduct at the amino terminus of the beta-chain as well as the carboxylate of carboxymethyl group at the same site are in a geometrical orientation that favors the formation of an intrachain ionic interaction with the epsilon-amino group of Lys-82(beta). On the other hand the stereochemistry of a carboxylate ion of galacuronic acid on Val-1(beta) appears to be appropriate to form either an intrachian salt bridge with epsilon-amino group of Ly2-82(beta) of the same chain (intrachain) or alternatively an interchain salt bridge involving the epsilon-amino group of Lys-82(beta) of the trans chain. We speculate that the latter, i.e. trans configuration is favored as a result of the potential of D-galacturonic acid bound to Val-1(beta) to form an additional hydrogen bond with trans His-143(beta).

Alkylation↗
PubMed1994

Recombinant hemoglobin A produced in transgenic swine: structural equivalence with human hemoglobin A.

Recombinant human hemoglobin A produced by coexpressing human alpha and beta globin genes in swine, and purified from the lysate of transgenic swine has been subjected to detailed protein chemical analysis. These structural studies involving laser desorption mass spectrometry, separation of globin chains by RPHPLC, amino terminal sequence analysis of the isolated globin chains, the tryptic peptide mapping of the purified globin chains and the amino acid composition analysis of the purified tryptic peptides of globin chains have established the primary structural equivalence of the globin chains of the transgenic swine derived hemoglobin A with that of human hemoglobin A. These results demonstrate that the transgenic swine system correctly translates the human alpha and beta globin m-RNA; carries out the correct cotranslational processing of globin chains, and does not introduce any unwanted post translational modifications into the mature chains. Thus, the transgenic swine expression system is an excellent approach for the production of HbA for developing an effective hemoglobin based oxygen carrier.

Amino Acid Sequence↗
PubMed1994

Bissulfosuccinimidyl esters of aliphatic dicarboxylic acids: a new class of 'affinity directed' beta beta crosslinkers of HbA.

The potential of sulfosuccinimidyl ester of suberic acid as an intramolecular crosslinker of HbA, directed to the positive charge rich domain of the protein (DPG pocket) has been investigated. The suberate ester introduced crosslinks between the beta-chains and inhibited the dissociation of HbA into alpha beta dimers. The facile crosslinking reaction seen with this suberate ester as compared to the absence of crosslinking with the diaspirin derivative of suberic acid suggests the strong 'steering' influence of the sulfosuccinimidyl moiety of the reagent to the targeted site. The application of this crosslinking approach in the preparation of Hb based blood substitutes is discussed.

Binding Sites↗
PubMed1993

Molecular basis of the inhibition of beta s-chain-dependent polymerization by mouse alpha-chain. Semisynthesis of chimeras of human and mouse alpha-chains.

The transgenic mouse models expressing beta s-globin genes do not fully exhibit the sickling phenotype, primarily as a result of the inhibition of beta s-chain-dependent polymerization by the mouse alpha-chains. The mouse alpha-chain differs from the human alpha-chain at 19 sequence locations. Of these, only alpha 78 and alpha 116 are the known hemoglobin (Hb) S polymer contact sites. To define whether the inhibition of polymerization by the mouse alpha-chain is solely a consequence of the differences at these two sites or additional sites of sequence differences are also involved, we have constructed chimeric alpha-chains by employing the alpha-globin semisynthetic reaction (Sahni, G., Cho, Y. J., Iyer, K. S., Khan, S. A., Seetharam, R., and Acharya, A. S. (1989) Biochemistry 28, 5456-5461). Mouse alpha 1-30 was spliced with human alpha 31-141 using endoproteinase Glu-C to generate a chimeric alpha-globin (alpha MH) containing eight of the 19 sequence differences of mouse alpha-globin. Similarly, human alpha 1-30 was spliced with mouse alpha 31-141 to generate another chimeric alpha-globin (alpha HM) containing 11 sequence differences. The respective chimeric globins were purified, reconstituted with heme and beta s-chain into tetrameric hemoglobin, and the tetramers were purified by ion-exchange chromatography. The inhibitory potential of the chimeric alpha MH-chain on the polymerization is 10-fold lower than that of the mouse alpha-chain. The absence of the alpha 31-141 region of the mouse alpha-chain relieves only a portion of the inhibition. The inhibitory potential of alpha MH contributed by the mouse alpha 1-30 segment is significant although none of the sequence differences in this segment are located at any of the implicated polymer contact sites. The chimeric alpha HM-chain also inhibits the polymerization, but the extent of inhibition is again lower (4-fold) than that of the full-length mouse alpha-chain. The results demonstrate that the inhibitory potential of mouse alpha-chains involves the sequence differences from both the alpha 1-30 and alpha 31-141 regions. Besides, since the sum of the inhibitory potential of either of these chimeric alpha-chains is lower than that of the intact mouse alpha-chains, we speculate that conformational changes that require the copresence of sequence differences in both portions of the mouse alpha-chain also contribute to the inhibitory propensity of the mouse alpha-chain.

Animals↗
PubMed1992

Amadori rearrangement potential of hemoglobin at its glycation sites is dependent on the three-dimensional structure of protein.

The site selectivity of nonenzymic glycation of proteins has been suggested to be a consequence of the Amadori rearrangement activity of the protein at the respective glycation sites [Acharya, A. S., Roy, R. P., & Dorai, B. (1991) J. Protein Chem. 10, 345-358]. The catalytic activity that determines the potential of a site for nonenzymic glycation is the propensity of its microenvironment to isomerize the protein bound aldose (aldimine) to a protein bound ketose (ketoamine). The catalytic power of the microenvironment of the glycation sites could be endowed to them either by the amino acid sequence (nearest-neighbor linear effects) or by the higher order structure (tertiary/quarternary) of the protein (nearest-neighbor three-dimensional effect). In an attempt to resolve between these two structural concepts, the glycation potential of Val-1(alpha) and Lys-16(alpha), the residues of hemoglobin A exhibiting the least and the highest isomerization activity in the tetramer, respectively, has been compared in the segment alpha 1-30, isolated alpha-chain, and the tetramer. When alpha-chain is used as the substrate for the nonenzymic glycation, the influence of the quaternary structure of the tetramer will be absent. Similarly, the contribution of the tertiary and quaternary structure of the protein will be absent when alpha 1-30 is used as the substrate. The microenvironment of Lys-16(alpha) exhibited hardly any Amadori rearrangement activity in the segment alpha 1-30. The tertiary structure of the alpha-chain induces a considerable degree of catalytic activity to the microenvironment of Lys-16(alpha) to isomerize the aldimine adduct at this site.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗