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PubMed1995

Complement activation by liposome-encapsulated hemoglobin in vitro: the role of endotoxin contamination.

Incubation of liposome-encapsulated Hb (LEH) with rat serum at 37 degrees C led to accelerated decay of serum hemolytic complement (C) activity (CH50/ml). Empty liposomes (L) caused less decrease of CH50/ml, whereas free Hb had no effect on C activity. The LEH- and L-induced increases in C consumption were unlikely a consequence of endotoxin (LPS) contamination, as spiking of rat serum with LPS caused reduction in C only at levels significantly higher than those detectable in LEH or L. LPS-induced C consumption was not potentiated by free hemoglobin.

Animals↗
PubMed1992

Relative bioavailability of iron in carbonyl iron and complex ferric orthophosphate to rat.

The relative biological availability (RBV of FeSO4.7H2O = 100%) of carbonyl iron and complex ferric orthophosphate in flour and bread baked with this flour was determined in a rat hemoglobin repletion assay. Hemoglobin iron gain and iron intake during repletion were used as dose-response parameters, and the relative biological values were assessed by the slope-ratio method. The RBV of carbonyl iron in flour was not calculated because the statistical validity of the slope-ratio method was not fulfilled. The RBVs of all the tested iron sources were significantly lower than that of the ferrous sulphate standard (p less than 0.01). The RBV for complex ferric orthophosphate in flour was 45 +/- 8%, and for complex ferric orthophosphate and carbonyl iron in bread 36 +/- 7% and 35 +/- 7%, respectively. There were no differences in the bioavailability of carbonyl iron and complex ferric orthophosphate (p greater than 0.01). Baking did not effect the bioavailability of complex ferric orthophosphate (p greater than 0.01).

Animals↗
PubMed1993

DNA polymorphisms associated with Hb D-Los Angeles [beta 121(GH4)Glu-->Gln] in southern Italy.

We detected Hb D-Los Angeles [beta 121(GH4)Glu-->Gln], the most common hemoglobin variant after Hb S and Hb Lepore-Boston, in six unrelated families in Southern Italy. Ten patients were studied; eight patients were heterozygotes and two were compound heterozygotes for the hemoglobin variant and the beta-thalassemia codon 39 (C-->T) nonsense mutation. The beta-globin gene sequence was characterized by polymerase chain reaction direct sequencing; restriction fragment length polymorphisms were defined by Southern blot analysis. The gene variant, due to the GAA-->CAA substitution at codon 121, was found in association with the 5' subhaplotype [+ - - - -] and the beta-globin gene framework 1; in addition, it was found to be associated with the absence of Ava II/phi beta and Xmn I/5'G gamma, and with the presence of Hpa I/3' beta. This restriction fragment length polymorphism haplotype is common in the Mediterranean area as well as in other populations. The findings are equally compatible with an independent origin in the Mediterranean area or with origin in Asia and subsequent spread to Italy.

Base Sequence↗
PubMed2006

Slow ligand binding kinetics dominate ferrous hexacoordinate hemoglobin reactivities and reveal differences between plants and other species.

Hexacoordinate hemoglobins are found in many living organisms ranging from prokaryotes to plants and animals. They are named "hexacoordinate" because of reversible coordination of the heme iron by a histidine side chain located in the heme pocket. This endogenous coordination competes with exogenous ligand binding and causes multiphasic relaxation time courses following rapid mixing or flash photolysis experiments. Previous rapid mixing studies have assumed a steady-state relationship between hexacoordination and exogenous ligand binding that does not correlate with observed time courses for binding. Here, we demonstrate that this assumption is not valid for some hexacoordinate hemoglobins, and that multiphasic time courses are due to an appreciable fraction of pentacoordinate heme resulting from relatively small equilibrium constants for hexacoordination (K(H)). CO binding reactions initiated by rapid mixing are measured for four plant hexacoordinate hemoglobins, human neuroglobin and cytoglobin, and Synechocystis hemoglobin. The plant proteins, while showing a surprising degree of variability, differ from the others in having much lower values of K(H). Neuroglobin and cytoglobin display dramatic biphasic time courses for CO binding that have not been observed using other techniques. Finally, an independent spectroscopic quantification of K(H) is presented that complements rapid mixing for the investigation of hexacoordination. These results demonstrate that hexacoordination could play a much larger role in regulating affinity constants for ligand binding in human neuroglobin and cytoglobin than in the plant hexacoordinate hemoglobins.

Binding Sites↗
PubMed2005

Synthesis and antimalarial activity of E-2-quinolinylbenzocycloalcanones.

A series of E-2-quinolinylbenzocycloalcanones 5-21 were prepared and evaluated for their activity to inhibit beta-hematin formation and the hydrolysis of hemoglobin in vitro. Positive compounds for both assays were also tested for their efficacy in rodent Plasmodium berghei. Compounds 6, 16, 19, and 20, were the most promising. Inhibition of beta-hematin formation was minimal when a hydrogen or methoxy groups were present on the position 8 of the quinoline and position 4' of the indanone ring as it appeared for compounds 5, 7-15, 17, 18, and 21, and greatest with compounds (52%) and (90%) with a substitution of methoxy on position 6 and 7 or methyl on position 8 of the quinoline nucleus and methoxy or methyl groups on position 4' of the indanone. The most active compound to emerge from this study is 2-chloro-8-methyl-3-[(4'-methoxy-1'-indanoyl)-2'-methyliden]-quinoline 20 effective as antimalarial that target beta-hematin formation and the inhibition of the hydrolysis of hemoglobin in vitro together with a good survival in a murine malaria model, which should help delay the rapid onset of resistance to drugs acting at only a single site. Results with these assays suggest that quinolinylbenzocycloalcanones exert their antimalarial activity via multiple mechanisms.

Animals↗
PubMed2005

Recovery from iron deficiency in rats by the intake of recombinant yeast producing human H-ferritin.

OBJECTIVE: This study examined whether iron accumulated in ferritin-producing recombinant microbes is bioavailable to rats with iron deficiency. METHODS: Rats induced with iron deficiency were treated with iron preparations of ferrous ammonium sulfate, horse spleen ferritin, control yeast, and ferritin-producing recombinant yeast for 14 d. The bioavailability of iron was examined by measuring hemoglobin concentration, hematocrit value, and tissue iron stores. Differences between dietary groups were determined by one-way analysis of variance, and P < 0.05 was considered statistically significant. RESULTS: Based on hemoglobin concentration and hematocrit value, iron in ferrous ammonium sulfate, horse spleen ferritin, and ferritin-producing yeast were bioavailable to rats and cured iron deficiency. The efficacy of ferritin and ferritin-producing yeast was also confirmed in establishing tissue iron stores after induction of iron deficiency. CONCLUSIONS: The iron sources of ferritin and ferritin-producing yeast were as effective in recovery from iron deficiency as the iron compounds of ferric citrate and ferrous ammonium sulfate. The results suggest that the iron stored in the ferritin of recombinant yeast is bioavailable, and that recombinant yeast may contribute widely as a source of iron to resolve the global problem of iron deficiency.

Analysis of Variance↗
PubMed1965

The oxygen equilibrium of mammalian hemoglobin. Some old and new physicochemical studies.

The three chief physicochemical theories of the oxygen-hemoglobin equilibrium in vogue 40 years ago still influence current thought on the problem. Although the Hill theory lost its fundamental basis some 40 years ago, the famous empiric equation to which it gave rise is still much used, as a useful phenomenological expression, only involving two disposable constants. The Haldane theory, of which a difference in aggregation of oxygenated and deoxygenated hemoglobin was a fundamental feature, lay for many years dormant but has recently had an astonishing reawakening through the work on lamprey hemoglobin, which clearly reveals such differences in aggregation. Lamprey hemoglobin might thus be called a "Haldane type" hemoglobin. Adair's four-stage intermediate compound theory still seems applicable in the case of hemoglobins such as those of sheep, whose tetramer molecules do not tend to dissociate into dimers, and which might therefore be called "Adair type" hemoglobins. Horse and human hemoglobins appear to reveal both "Haldane" and "Adair" behaviour. The effects of pH, temperature, and protein concentration on the oxygen-equilibrium of sheep hemoglobin are summarised, and it is shown that, although the equilibrium curves are often isomorphous over their middle range, intensive work at the top and bottom of the curves reveals considerable differences in the relative effects of these factors on the several equilibrium constants of Adair's four intermediate equations. In the last section an account is given of preliminary experimental attempts to interpret the oxygen- and carbon monoxide-equilibrium curves of whole human blood, under physiological conditions in terms of the Adair intermediate compound hypothesis.

Animals↗
PubMed2000

Detection of phase variation in expression of proteins involved in hemoglobin and hemoglobin-haptoglobin binding by nontypeable Haemophilus influenzae.

Haemophilus influenzae can utilize different protein-bound forms of heme for growth in vitro. A previous study (I. Maciver, J. L. Latimer, H. H. Liem, U. Muller-Eberhard, Z. Hrkal, and E. J. Hansen. Infect. Immun. 64:3703-3712, 1996) indicated that nontypeable H. influenzae (NTHI) strain TN106 expressed a protein that bound hemoglobin-haptoglobin and was encoded by an open reading frame (ORF) that contained a CCAA nucleotide repeat. Southern blot analysis revealed that several NTHI strains contained between three and five chromosomal DNA fragments that bound an oligonucleotide probe for CCAA repeats. Three ORFs containing CCAA repeats were identified in NTHI strain N182; two of these ORFs were arranged in tandem. The use of translational fusions involving these three ORFs and the beta-lactamase gene from pBR322 revealed that these three ORFs, designated hgbA, hgbB, and hgbC, encoded proteins that could bind hemoglobin, hemoglobin-haptoglobin, or both compounds. Monoclonal antibodies (MAbs) specific for the HgbA, HgbB, and HgbC proteins were produced by immunizing mice with synthetic peptides unique to each protein. Both HgbA and HgbB were readily detected by Western blot analysis in N182 cells grown in the presence of hemoglobin as the sole source of heme, whereas expression of HgbC was found to be much less abundant than that of HgbA and HgbB. The use of these MAbs in a colony blot radioimmunoassay analysis revealed that expression of both HgbA and HgbB was subject to phase variation. PCR and nucleotide sequence analysis were used in conjunction with Western blot analyses to demonstrate that this phase variation involved the CCAA repeats in the hgbA and hgbB ORFs.

Amino Acid Sequence↗
PubMed2007

Influence of the protein matrix on intramolecular histidine ligation in ferric and ferrous hexacoordinate hemoglobins.

Present in most organisms, hexacoordinate hemoglobins (hxHbs) are proteins that have evolved the capacity for reversible bis-histidyl heme coordination. The heme prosthetic group enables diverse protein functionality, such as electron transfer, redox reactions, ligand transport, and enzymatic catalysis. The reactivity of heme is greatly effected by the coordination and noncovalent chemical environment imposed by its connate protein. Of considerable interest is how the hxHb globin fold achieves reversible intramolecular coordination while still enabling high-affinity binding of oxygen, nitric oxide, and other small ligands. Here we explore this question by examining the role of the protein matrix on coordination behavior in a group of hxHbs from animals, plants, and bacteria, including human neuroglobin and cytoglobin, a nonsymbiotic hemoglobin from rice, and a truncated hemoglobin from the cyanobacterium Synechocystis. This is done with a set of experiments measuring the reduction potentials of each wild-type hxHb and its corresponding mutant protein where the reversibly bound histidine (the distal His) has been replaced with a noncoordinating side chain. These reduction potentials, coupled with studies of the mutant proteins saturated with exogenous imidazole, enable us to assess the effects of the protein matrices on histidine coordination. Our results show significant variation among the hxHbs, demonstrating flexibility in the globin moiety's ability to regulate reversible coordination. This regulation is particularly evident in the plant nonsymbiotic hemoglobins, where ferric state histidine coordination affinity is substantially lowered by the protein matrix.

Animals↗
PubMed2005

Hemoglobin I from Lucina pectinata: a model for distal heme-ligand control.

Lucina pectinata hemoglobin I (HbI), which is a ferric sulfide-reactive hemeprotein, contains a distal pocket characterized by the presence of GlnE7 and PheB10. To elucidate the structural-functional properties of HbI, oxygen binding kinetics and FTIR studies with recombinant HbI (rHbI) and a set of mutants were conducted using CO and CN- as sensors of the hemeprotein environment. Three nuCO modes were observed for rHbI at 1936 cm(-1) (A3, closed conformer) 1950 cm(-1) (A1,2, closed conformer) and 1960 cm(-1) (A0, open conformer). These nuCO were affected by substitution of GlnE7 and PheB10 in the CO complexes. The contribution of GlnE7 is demonstrated when this residue is replaced with Asn, Val or His. For instance, decreasing the positive electrostatic environment with GlnE7Val, causes an increase of 65% in the population of A0 and the disappearance and 55% reduction of the population of the A1,2 and A3 respectively. The contribution of PheB10 to the stabilization of ligands is also observed in the Leu and Tyr mutants. The PheB10Leu mutation produced an 8% decrease in the population of the A3 conformer while that of the A1,2 configuration increased by 30%. This suggests that GlnE7 and PheB10 contribute to the A3 conformer stabilizing the CO in a closed configuration. With CN- as probe no substantial differences in the nuCN was observed upon substitution of GlnE7 by Val while a slight down shift in the nuCN from 2120 cm(-1) to 2117 cm(-1) was observed in the PheB10Leu mutant. This implies that in HbICN GlnE7 moves away from the binding site while PheB10 remains in the vicinity of the bound CN-. Here, a mechanism in which the flexibility of the distal protein matrix coupled with hemeporphyrin movement toward a different configuration is suggested as an important process in the H2S transport and delivery in hemoglobin I.

Amino Acid Sequence↗
PubMed1995

Mechanism of ligand binding to Ni(II)-Fe(II) hybrid hemoglobins.

The geminate and bimolecular binding of CO, O2 and NO to [alpha-Ni(II)]2-[beta-Fe(II)]2 and [alpha-Fe(II)]2-[beta-Ni(II)2] hybrid hemoglobins has been studied. Biomolecular reactions: At pH 6.6 and 20 degrees both hybrids bind CO at 0.15 x 10(6) M-1 s-1. Reactions with oxygen: At pH 6.6 the on rates are 4.8 and 7.5 x 10(6) M-1 S-1 for alpha- and beta-hybrids, respectively; the off rate is approximately 2 x 10(3) S-1 for both. At pH 8 the alpha-Fe shows cooperativity whereas the beta-hybrid does not. Nanosecond geminate reactions: Faster bimolecular rates correlate with larger geminate amplitudes; thus alpha-Fe hybrids have larger amplitudes, and O2 geminate amplitudes are larger than those with CO. At pH 8.50% of O2 recombines with the alpha-hybrid. With NO, nanosecond geminate recombination is observable only with the beta-hybrid. Picosecond reactions: alpha-Hybrids show picosecond recombination of O2. With NO, alpha-hybrids recombine at 30 ns-1, beta-hybrids at 0.3 ns-1. The NO picosecond rates correlate with the molecular dynamics which shows ligands leaving the beta-Fe atom early and regularly, but remaining near the alpha-Fe atom. The results may be explained by assuming an interaction between the alpha-subunits giving rise to a high-affinity faster-reacting form, whereas the beta-subunits only become fast-reacting when an R-T conformation change analogous to that of hemoglobin A takes place. A third allosteric state is postulated to explain the results.

Allosteric Regulation↗
PubMedDate not supplied

[The mechanism of metabolic denitration of nitroheterocyclic compounds].

It has been found that denitration of nitroheterocyclic drugs (NHCC) in mouse liver homogenate is one of the pathways of their biotransformation. This process is accompanied by the release of NO and NO-heme iron complex formation. The yield of complex increases linearly with time of NHCC incubation with liver homogenate and depends on NHCC structure. The ESR spectrum of the complex represents a superposition of spectra of NO with hemoglobin and NO with the other heme-containing proteins. NHCC denitration is inhibited by metyrapone, which is an evidence of cytochrome P-450 involvement in their metabolic denitration.

Animals↗