Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:Q0Z944 (hemoglobin)
 63,986 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Position beta 82 in human hemoglobin (Hb) is normally occupied by lysine, a positively charged residue that is involved in the binding of anionic cofactors. This residue is substituted by a neutral residue in Hb Providence Asn and by a negatively charged residue in Hb Providence Asp. Hb Providence Asp shows more differences from Hb A than does Hb Providence Asn in studies of the kinetics and equilibria of ligand binding. For both forms, homotropic (cooperative) interactions are normal with n values of 2.5 to 2.7, while heterotropic (pH and anion) interactions are reduced greatly. The reduction in anion sensitivity is attributed to the absence of a positive residue at position beta 82. Reduction in pH sensitivity may be due to a ligand-linked change in the pK of a neighboring residue, beta 143 histidine, which normally is not a Bohr group. This change in pK would act in opposition to the normal Bohr effect. Reduction in the net positive charge of the central cavity has a further consequence. Relative to Hb A, both Hb Providence Asn and Hb Providence Asp show decreased oxygen affinities at neutral pH in the absence of cofactors. This suggests that in Hb A the binding of anionic cofactors directly influences the oxygen affinity by neutralizing the charged groups of the diphosphoglycerate binding site and thus stabilizing the low affinity (T) conformation. From pH 6 to 9 in the presence of 1 M NaCl, where all the charged groups may be masked, the oxygen-binding properties of Hb A and the Hb Providence mutants are identical. Moreover, subunit dissociation of the liganded Hb Providence mutants appears to be increased, as is known to occur for Hb A in the presence of high salt. The results obtained with Hb Providence Asn and Hb Providence Asp illustrate how single amino acid substitutions can modify hemoglobins' pH and anion interactions without altering cooperative interactions between subunits. The alteration in cofactor effects observed with these mutants also illustrates differences between the allosteric effects induced by organic and inorganic anions.
 ...
PMID:Hemoglobin providence. Functional consequences of two alterations of the 2,3-diphosphoglycerate binding site at position beta 82. 1 72

Carriers of hemoglobin Providence have three types of beta chain in their hemolysates. The two abnormal chains have asparagine (Providence N, Prov N) or aspartic acid (Providence D) at position beta 82, instead of lysine. In vitro, only two beta chains are synthesized by reticulocytes of carriers, betaA and betaProv N. In vivo studies showed that the specific activity of Providence N was initially 10-fold higher than that of Providence D; the specific activities of the two labeled hemoglobins were approximately equal 5 wk after injection of isotope. Oxygen affinity of carriers' blood was somewhat increased, but they were not polycythemic. The affinity of the purified hemoglobins Providence was decreased. Addition of 2, 3 diphosphoglycerate had little effect on the affinity of either hemoglobin component, and addition of inositol hexaphosphate produced no change in the affinity of Providence D. These studies demonstrate that Providence N is deamidated to Providence D during the life span of the erythrocyte, and suggest this finding may represent only an easily observed prototype of posttranslational modification of proteins in general. Despite and abnormal P50 of the blood, oxygen transport is probably normal in carriers of the abnormal hemoglobins.
 ...
PMID:Postsynthetic deamidation of hemoglobin Providence (beta 82 Lys replaced by Asn, Asp) and its effect on oxygen transport. 1 73

Most of the bifunctional reagents in protein chemistry possess a strongly hydrophobic backbone, derived from aliphatic or aromatic hydrocarbons. Even bifunctionals of more than 30 A in length of this sort form intramolecular bridges preferentially. In recent years, the intermolecular crosslinking of physiological protein aggregates has gained in importance. As shown in the crosslinking of hemoglobin with two sets of hydrophobic and strongly hydrophilic reagents, derived from azo dyes and tartaric acid, respectively, in this case it is not primarily the length of the bifunctional, but the hydrophilic structure that will enhance intermolecular crosslinking. Artificial dimers of native structure may be obtained. For the crosslinking of RNA to protein, we have synthesized a new reagent, 3-(2-bromo-3-oxobutane-1-sulphonyl)-propionic acid p-nitrophenyl ester. In a two step reaction, it is attached to adenine and cytosine moieties at pH 6 first, and to lysine side chains at pH 7,5. The reagent has been applied to the poly-A sequence of globin messenger RNA nucleoprotein.
 ...
PMID:Comparison of hydrophobic and strongly hydrophilic cleavable crosslinking reagents in intermolecular bond formation in aggregates of proteins or protein-RNA. 2 35

The most abundant minor hemoglobin component of human hemolysate is Hb A1c, which has glucose bound to the N-terminus of the beta chain by a ketoamine linkage. Hb A1c is formed slowly and continuously throughout the 120 day lifespan of the red cell. It can be synthesized in vitro by incubating purified hemoglobin with 14C-glucose. Other minor components, Hb A1a1 and Hb A1a2 are adducts of sugar phosphates at the N-terminus of the beta chain. Hb A1b contains an unidentified nonphosphorylated sugar at the beta N-terminus. In addition, a significant portion of the major hemoglobin component (Hb Ao) is also glycosylated by a glucose ketoamine linkage at other sites on the molecule, including the N-terminus of the alpha chain and the epsilon-amino group of several lysine residues on both the alpha and the beta chains. The results indicate that the interaction of glucose and hemoglobin is rather nonspecific and suggests that other proteins are modified in a similar fashion.
 ...
PMID:Nonenzymatic glycosylation of human hemoglobin at multiple sites. 12 95

The increased level of the glycosylated hemoglobin (hemoglobin A1c) in the diabetic patient has proved to be an interesting clue to understanding the biochemical basis of the sequelae of diabetes. This minor hemoglobin, which arises as nonenzymatic postsynthetic addition of glucose to hemoglobin A, acts as an indicator molecule for the glucose environment over a 3-5-wk period prior to measurement. Reasoning that a similar glycosylation reaction could be occurring with other body proteins, we have studied the ocular lens. The lens, like the erythrocyte, is not dependent on insulin for glucose concentration in the extracellular milieu that would be elevated in the diabetic state. These studies have revealed that a high glucose in vivo or an increased glucose or glucose-6-phosphate concentration in vitro leads to the glycosylation of epsilon-amino groups of lysine residues in bovine and rat lens crystallins. This glycosylation imparts an increased susceptibility of the crystallins to sulfhydryl oxidation. Disulfide crosslinks result in the formation of high molecular weight aggregates and an opalescence of the crystallin solutions.
 ...
PMID:Role of nonenzymatic glycosylation in the development of the sequelae of diabetes mellitus. 12 96

A group of abundant (15% of the soluble protein) nonhemoglobin proteins was isolated from the primitive (embryonic) red cells found in tadpoles, using the cationic properties of the proteins at pH 8.6 to separate them from hemoglobin and other red cell proteins. The cathodal proteins (CP) were resolved into five components, and the two most predominant proteins were separated and characterized. Purified CP-1b and CP-2 had an amino acid composition similar to that of unfractionated cathodal proteins and to each other, except for small variations in the lysine and half-cystine content. The molecular weight of the purified CP-1b and CP-2 was 13 to 14,000, determined by gel filtration chromatography and electrophoresis in the presence of sodium dodecyl sulfate. Cathodal proteins were immunologically related although there were quantitative differences in reactivity. The concentration of cathodal proteins in primitive (embryonic) red cells was 100 times that in definitive (adult) red cells coincided with the replacement of primitive red cells. The synthesis of the cathodal proteins appeared to continue throughout the life of the primitive red cells; when hemoglobin synthesis declined in primitive red cells, approximately half of the protein synthesized by the cells was cathodal protein. Although the function of the cathodal proteins is as yet unknown, the data suggest that the cathodal proteins are a unique characteristic of erythroid differentiation in early development.
 ...
PMID:Cathodal proteins from primitive (embryonic) red cells of amphibia. Isolation and characterization. 23 4

The chemical modification of hemoglobin by aspirin (ASA) has been studied, both in intact human red cells and in purified hemoglobin solutions. After incubation of red cells with 20 mM [acetyl-1minus14C]ASA, incorporation of radioactivity into hemoglobin was observed in agreement with the results of Klotz and Tam (1973. Proc. Natl. Acad. Sci. U. S. A. 70: 1313-1315). In contrast, no labeling of hemoglobin was seen when [carbosyl-14-C]ASA was used. These results indicate that ASA acetylates hemoglobin. The acetylated hemoglobin was readily separated from unmodified hemoglobin by both gel electrofocusing and by column chromatography. Quantitation of the extent of acetylation by densitometric scanning of gels agreed very well with estimates obtained from radioactivity measurements. Hemolysates prepared from red cells incubated with ASA showed normal oxygen affinity and heme-heme interaction. Purified acetylated hemoglobin had a slightly increased oxygen affinity and decreased heme-heme interaction. There was no difference in the rate of acetylation of oxy- and deoxyhemoglobin. ASA acetylated column-purified hemoglobin A more readily than hemoglobin in crude hemolysate, but less rapidly than purified human serum albumin. The rate of acetylation of hemoglobulin increased with pH up to approximately pH 8,5. Structural studies were done on hemoglobin incubated with 2.0 mM and 20 mM [acetyl-1-14-C]ASA. Alpha- and beta-chains were acetylated almost equally. Tryptic digests of purified acetylated subunits were fingerprinted on cellulose thin layer plates and autoradiographed. Both alpha- and beta-chains showed a number of radioactive spots that were either ninhydrin negative or weakly ninhydrin positive. These results indicate that hemoglobin is acetylated at a number of sites, probably at the epislon-amino group of lysine residues. To determine whether ASA acetylates hemoglobin in vivo, hemolysates of 14 patients on long-term high-dose ASA therapy were analyzed by gel electrofocusing and compared to specimens of individuals not receiving ASA. The ASA-treated group had a twofold increase in a minor hemoglobin component having an isoelectric point lower than that of hemoglobin A, and indistinguishable from the minoe component which appears when hemoglobin is incubated with ASA in vitro.
 ...
PMID:The acetylation of hemoglobin by aspirin. In vitro and in vivo. 23 37

Concentrations of DL-glyceraldehyde between 5 and 20 mM reduce the sickling of S/S erythrocytes even in the complete absence of oxygen; at 10 mM glyceraldehyde the increase in the number of normal cells ranges from 20 to 40%. The inhibition of sickling was both concentration- and time-dependent and was not reversed by repeated washings with buffer. Incubation of erythrocytes with increasing concentrations of glyceraldehyde resulted in only a small increase in the oxygen affinity, a moderate reduction in the Hill coefficient, a substantial increase in the minimum gelling concentration, and modification of up to two lysine residues per hemoglobin molecule.
 ...
PMID:Inhibition of erythrocyte sickling in vitro by DL-glyceraldehyde. 26 89

Reticulocytes, like other cells, selectively degrade certain abnormal proteins by an energy-dependent process. When isolated rabbit reticulocytes incorporate the valine analog 2-amino-3chlorobutyric acid (ClAbu) in place of valine, they produce an abnormal globin that is degraded with a half-life of 15 min. Normal hemoglobin, in contrast, undergoes little or no breakdown within these cells. Cell-free extracts from reticulocytes have been shown to rapidly hydrolyze these abnormal proteins. The degradative system is located in the 100,000 X g supernatant, has a pH optimum of 7.8, and does not appear to be of lysosomal origin. This breakdown of analog-containing protein was stimulated severalfold by ATP, and slightly by ADP. AMP and adenosine-3':5'-cyclic monophosphate had no significant effect on proteolysis. Experiments with ATP analogs suggest that the terminal high energy phosphate is important in the degradative process. Proteolysis in the cell-free system and in intact reticulocytes was inhibited by the same agents (L-l-tosylamido-2-phenyl-ethylchloromethyl ketone, N-alpha-p-tosyl-L-lysine chloromethyl ketone, N-ethylmaleimide, iodoacetamide, and o-phenanthroline). In addition, the relative rates of degradation of several polypeptides in the cell-free extracts paralleled degradatives rates within cells. Thus, a soluble nonlysosomal proteolytic system appears responsible for the energy-dependent degradation of abnormal proteins in reticulocytes.
 ...
PMID:A soluble ATP-dependent proteolytic system responsible for the degradation of abnormal proteins in reticulocytes. 26 94

Immunochemical homogeneous human pepsinogen I-group (PgI) was purified by solid immunoadsorbent and by DEAE-chromatography from gastric mucosa. PgI contained five electrophoretic distinct bands at pH 8.2 but only four bands at pH 5.6. After acid activation human pepsin (PI) was separated from the inhibitory peptide by affinity chromatography using poly-L-lysine. Purified PgI contained 9-16% of the inhibitory peptide. The yield of PI was 64 to 85%. A 65% increase of specific activity was observed. PI demonstrated three bands in agar gel electrophoresis at pH 5.6. The pH range of PI was rather wide, showing two maxima at pH 2.0 and pH 3.0 with hemoglobin as substrate. Irreverisble inactivation of PI was observed at pH 7.0 and at a temperature of 60 degrees C. The Km-value of PI was 0.170 mmol as determined with N-acetyl-L-phenyl-alanyl-L-3,5 diiodotyrosine. The specific activity was 9.6 IU/mg (hemoglobin substrate) and 0.032 IU/mg (dipeptide substrate). Porc pepsinogen (PPg) and its activated pepsin (PP) was used for comparison. PP showed indentical elution patterns in affinity chromatography. In AEE PPg and PP demonstrated both two components at pH 5.6 with different electrophoretic mobilities. The pH optimum of PP was observed at pH 2.0. PP was slightly more sensitive in alkali and heat inactivation than human P. A higher Km-value of PP of 0.082 mmol and higher specific activity as compared to human PI was observed.
 ...
PMID:Characterization of human pepsin I obtained from purified gastric pepsinogen I. 38 70


1 2 3 4 5 6 7 8 9 10 Next >>