A micromethod for measuring the molar concentration of polyadenylated RNA in the presence of ribosomal RNA

A method has been developed for measuring the molar concentration of RNA and the mole fraction of polyadenylated RNA. Using known mixtures of globin mRNA and rRNA composed of 20 to 85% rRNA, the molar concentration of globin mRNA, a polyadenylated species, was determined in 45 min, with the consumption of less than 100 ng of total RNA. The technique is particularly well suited for determining the molar concentration of poly(A)+ RNA after chromatographic enrichment in columns of oligo(dT)-cellulose or poly(U)-Sepharose. The method makes possible the adoption of a molar standard.

Localization of low abundance DNA sequences in tissue sections by in situ hybridization

Specific DNA sequences were loaclized in the nuclei of paraffin-embedded mouse tissue sections with in situ hybridization using a biotinylated globin probe in conjunction with a streptavidin-alkaline phosphatase detection system. Globin inserts were clearly detected in the tissue sections of transgenic mice containing 1000, 120 or 5 copies of the exogenously introduced beta-globin genes. In addition, specific hybridization signal was also obtained for the endogenous complement of beta-globin genes in the tissue sections of normal mice. These results demonstrate that this hybridization procedure is very sensitive and should be useful for characterizing the distribution of low abundance DNA sequences in cells and tissue sections.

Hb Bicêtre or alpha 2 beta(2)63(E7)His----Pro in a white male: clinical observations over a period of 25 years

A description is given of clinical observations over a period of 25 years for a 26-year-old white male with a heterozygosity for the beta-chain variant, Hb Bicêtre, in which beta 63His is replaced by Pro. The variant was identified through analysis of tryptic peptides from a digest of the beta X-chain isolated by PCMB precipitation and purified by chromatography. Similarity between the clinical histories of the first (French) heterozygote and our patient was most striking, including improvement after splenectomy.

RNA splicing products formed with isolated fractions from HeLa cells are associated with fast-sedimenting complexes

Three fractions (designated Ia, Ib, and II) have been isolated from HeLa cell nuclear extracts that are required for splicing of adenovirus and human beta-globin RNA transcripts in vitro. The incubation of two of the fractions (Ib and II) in the presence of ATP resulted in cleavage of precursor mRNA at the 5' splice site and formation of the intron-exon lariat. Addition of fraction Ia to the combination of Ib and II resulted in the formation of spliced RNA and the intron lariat. When fraction II was incubated with precursor RNA in the presence of ATP and the resulting products were sedimented through sucrose gradients, a 30S complex was detected that contained precursor RNA. The combination of fractions Ib and II resulted in the production of a 55S complex that contained the 5' exon as a prominent RNA species. The combination of fractions I (containing Ia and Ib) and II resulted in the formation of the 55S complex and material sedimenting between 40 S and 20 S, in which the predominant RNA species was spliced RNA.

Specific regions of the intervening sequences of beta-globin RNA are resistant to nuclease in 50S heterogeneous nuclear RNA-protein complexes

The specific assembly of heterogeneous nuclear RNA-protein complexes (hnRNPs) containing precursor beta-globin RNA was investigated by using the 50S hnRNP released from chicken reticulocyte nuclei by endogenous nuclease. The nuclease-resistant regions were mapped on adult beta-globin intervening sequences (IVS) at the resolution of nucleotides with an RNA mapping method [Patton, J. R. and Chae, C.-B. (1983) J. Biol. Chem. 258, 3991-3995]. We found that there is one 28-nucleotide-long nuclease-resistant region in the first IVS and there are four nuclease-resistant regions in the second IVS. Of particular interest is the presence in 50S hnRNP of a nuclease-resistant region (24-28 nucleotides long) in both IVS immediately upstream from the putative lariat branch site in an RNA splicing intermediate. Our results demonstrate that hnRNPs containing precursor beta-globin RNA are, like those containing mature beta-globin RNA, assembled in a site-specific manner.

X-ray crystallographic structure of the light-harvesting biliprotein C-phycocyanin from the thermophilic cyanobacterium Mastigocladus laminosus and its resemblance to globin structures

The structure of the biliprotein C-phycocyanin from the thermophilic cyanobacterium Mastigocladus laminosus has been determined at 3 A resolution by X-ray diffraction methods. Phases have been obtained by the multiple isomorphous replacement method. The electron density map could be improved by solvent flattening and has been interpreted in terms of the amino acid sequence. The protein consists of three identical (alpha-beta)-units which are arranged around a threefold symmetry axis to form a disc of approximate dimensions 110 A X 30 A with a central channel of 35 A in diameter. This aggregation form is supposed to be the same as that found in the rods of native phycobilisomes. Both subunits, alpha and beta, exhibit a similar structure and are related by a local twofold rotational axis. Each subunit is folded into eight helices and irregular loops. Six helices are arranged to form a globular part, whereas two helices stick out and mediate extensive contact between the subunits. The arrangement of the helices of the globular part resembles the globin fold: 59 equivalent C alpha-atoms have a root-mean-square deviation of 2 X 9 A. The chromophores attached to cystein 84 of the alpha- and beta-subunits are topologically equivalent to the haem. All three chromophores of C-phycocyanin, open-chain tetrapyrroles, are in an extended conformation. alpha 84 and beta 84 are attached to helix E (globin nomenclature), beta 155 is linked to the G--H loop. The shortest centre-to-centre distance between chromophores in trimer is 22 A.

Aromatic-aromatic interaction: a mechanism of protein structure stabilization

Analysis of neighboring aromatic groups in four biphenyl peptides or peptide analogs and 34 proteins reveals a specific aromatic-aromatic interaction. Aromatic pairs (less than 7 A between phenyl ring centroids) were analyzed for the frequency of pair type, their interaction geometry (separation and dihedral angle), their nonbonded interaction energy, the secondary structural locations of interacting residues, their environment, and their conservation in related molecules. The results indicate that on average about 60 percent of aromatic side chains in proteins are involved in aromatic pairs, 80 percent of which form networks of three or more interacting aromatic side chains. Phenyl ring centroids are separated by a preferential distance of between 4.5 and 7 A, and dihedral angles approaching 90 degrees are most common. Nonbonded potential energy calculations indicate that a typical aromatic-aromatic interaction has energy of between -1 and -2 kilocalories per mole. The free energy contribution of the interaction depends on the environment of the aromatic pair. Buried or partially buried pairs constitute 80 percent of the surveyed sample and contribute a free energy of between -0.6 and -1.3 kilocalories per mole to the stability of the protein's structure at physiologic temperature. Of the proteins surveyed, 80 percent of these energetically favorable interactions stabilize tertiary structure, and 20 percent stabilize quaternary structure. Conservation of the interaction in related molecules is particularly striking.

Regulation of messenger RNA stability in mouse erythroleukemia cells

The decay rates of several messenger RNA species were determined in mouse erythroleukemia cells. The t1/2 values for the actin and tubulin mRNAs were 16 to 26 hours and about seven hours, respectively. The globin mRNA, and two mRNA species subject to translation repression, the P40 and P21 mRNAs, were about as stable as the ribosomal RNA. A stable tubulin mRNA component also appeared to be present in the cells. Exposure of the cells to dimethylsulfoxide for 48 hours led to considerable increases in the rates of decay of all but the globin mRNA. The induction of erythroid differentiation caused by the drug appears to lead to activation of a mRNA-degradation process that affects individual species to different degrees. The newly synthesized actin and tubulin mRNAs lost their poly(A) rather rapidly. This was accompanied by accumulation of poly(A)-deficient mRNA chains, particularly in the case of actin mRNA. The steady-state distribution of mRNA components, determined by Northern blot analysis, also showed that the actin mRNA and one tubulin mRNA species have a high proportion of poly(A)-deficient molecules. The globin, P40 and P21 mRNAs showed little tendency to lose their poly(A) sequence. The steady-state globin and P40 mRNAs also had a low proportion of chains depleted of poly(A). For all five species, the proportions of poly(A)-deficient chains in newly synthesized mRNA were about the same in uninduced and induced cells, in spite of the large decreases in mRNA stability in the induced cells. The lack of correlation between tendency to lose poly(A) and rate of mRNA decay, and the large accumulation of poly(A)-deficient molecules in the cases of the actin and tubulin mRNAs suggest that the stability of mRNA is not determined solely by the presence of poly(A) on the RNA chains. The behavior of the untranslated species in induced and uninduced cells also fails to support the notion of a relationship between translation and mRNA decay.

Configuration of beta-globin messenger RNA in rabbit reticulocytes. Identification of sites exposed to endogenous and exogenous nucleases

Masked and exposed sites in rabbit beta-globin messenger RNA were identified through S1 nuclease mapping of RNase T1 cleavage sites. Sites exposed to this enzyme were compared in deproteinized polysomal RNA and in mRNA in its native configuration in reticulocyte extracts. The analysis showed that most of the 3' non-coding region is well accessible to the enzyme, both in deproteinized RNA and in the cell extract. A possible protecting function for the poly(A) sequence is suggested by the fact that molecules with very short poly(A) segments were cleaved preferentially in this region. The G residues in the 5' non-coding region were inaccessible to RNase T1. A highly sensitive site adjacent to the initiation AUG codon was evident in the deproteinized RNA. This site was far less accessible to the enzyme in the mRNA associated with ribosomes in the cell extract. The first 150 nucleotides in the coding region showed very little susceptibility to digestion by the enzyme, in deproteinized RNA as well as in the cell extracts. Preparations of untreated mRNA showed the occurrence of truncated molecules, apparently generated by cleavage by endogenous nucleases. These cleavages were most prevalent in the two non-coding regions. They occurred at sites containing A-U sequences in the 3' non-coding region, and at sites with different sequences in the 5' non-coding region. Incubation of cell extracts at 37 degrees C did not cause any increase in these endogenous cleavages. It is suggested that they may have been generated in the intact cells, possibly as part of the mRNA degradation process in maturing reticulocytes.

A simple method for the calculation of low energy packings of alpha-helices--a threshold approximation. I. The use of the method to estimate the effects of amino acid substitutions, deletions and insertions in globins

A simple method is developed for computing low energy packings in alpha-helical proteins. This method is based on a simplified representation of a protein molecule in which the backbone of the alpha-helix is represented by a cylinder and the side chains of the amino acids by hard spheres. The energy function includes hydrophobic, electrostatic and Van der Waals' interactions. This method is used to compute low energy packings of an assembly of the alpha-helices of a globin molecule. The effect of mutations, deletions and insertions of a single amino acid resulting in drastic distortion of the spatial structure of sperm whale myoglobin was studied. The results demonstrated that these events can produce a breakdown of the spatial structure of the protein molecule.

Correlation of sequence hydrophobicities measures similarity in three-dimensional protein structure

The degree of similarity in the three-dimensional structures of two proteins can be examined by comparing the patterns of hydrophobicity found in their amino acid sequences. Each type of amino acid residue is assigned a numerical hydrophobicity, and the correlation coefficient rH is computed between all pairs of residues in the two sequences. In tests on sequences from two properly aligned proteins of similar three-dimensional structures, rH is found in the range 0.3 to 0.7. Improperly aligned sequences or unrelated sequences give rH near zero. By considering the observed frequency of amino acid replacements among related structures, a set of optimal matching hydrophobicities (OMHs) was derived. With this set of OMHs, significant correlation coefficients are calculated for similar three-dimensional structures, even though the two sequences contain few identical residues. An example is the two similar folding domains of rhodanese (rH = 0.5). Predictions are made of similar three-dimensional structures for the alpha and beta chains of the various phycobiliproteins, and for delta hemolysin and melittin.

Hemoglobin tertiary structural change on ligand binding. Its role in the co-operative mechanism

Analysis of the tertiary structural alterations in hemoglobin induced by ligand binding demonstrates that an allosteric core composed of the heme, histidine F8, the FG corner and part of the F-helix plays an essential role in co-operativity. This conclusion is based on structural and spectroscopic data and theoretical studies of hemoglobin chains. The methodology employed in the calculations is presented with details of the empirical energy function. Energy minimized structures of the unliganded hemoglobin chains, which serve as reference systems for the analysis, are described. To determine the structural changes induced by ligand binding, the effects of Fe--N bond shortening and of heme translation and tilting perturbations are examined. Energy minimization in the presence of the perturbations serves to provide information concerning the globin structural modifications produced by them. The validity of the results is supported by comparisons with the X-ray data of Anderson, Pulsinelli, Baldwin and Chothia on tertiary changes in the hemoglobin subunits. Internal to the allosteric core, there appear to be two stable positions for its elements: one of these corresponds to the liganded and the other to the unliganded species. The unliganded geometry fits without strain into the deoxy tetramer, while the liganded one fits without strain into the oxy tetramer. On ligation of a subunit in the deoxy tetramer, the structural changes within the allosteric core are in the direction of those found in going from the unliganded deoxy to the liganded oxy system, although they are reduced by the presence of constraints due to the other subunits in the deoxy tetramer. In addition, the quaternary constraints in the deoxy tetramer prevent the large overall displacement of the allosteric core that occurs in the transition to the liganded oxy tetramer. The coupling between the changes internal to the allosteric core, produced on ligation and the overall displacement of the core that accompanies the quaternary transition, is an essential element of the co-operative mechanism. As shown in previous work (Gelin & Karplus, 1977), the proximal histidine serves as the link between the position of the heme and the F-helix; the asymmetric orientation of the histidine in the deoxy structure, coupled with contributions from other heme-protein interactions, appears to initiate the tertiary structural changes induced by ligand binding. The reduced oxygen affinity of hemoglobin results not from tension on the heme in the unliganded structure (there is none) but instead from strain in the liganded subunit of the tetramer within the deoxy quaternary structure.(ABSTRACT TRUNCATED AT 400 WORDS)

Enzymatic methylation of inverted DNA repeats in the vicinity of the mouse beta-major globin gene

This paper examines the extent of enzymatic methylation in 5'-CCGG sequences of inverted repeats in DNA isolated from adult liver and bone marrow of DBA/2 mice, with special attention to the methylation of such sequences in the vicinity of the beta-major globin gene. Two thirds of inverted repeats contain 5'-AGCT and 5'-CCGG sequences, as found by a method based on the capability of inverted repeats of forming intramolecular duplexes under the conditions of "zero-time" reassociation. Methylation in internal cytosines of 5'-CCGG sequences of inverted DNA repeats differs between bone marrow and liver tissues. The beta-major globin gene was found in DNA covalently linked to inverted repeats. The enzymatic methylation of inverted repeats neighbouring the beta-major globin gene differs at HpaII recognition sites; the DNA of bone marrow tissue, in which this gene is expressed, is less methylated at such sites as compared to liver DNA.

Ion-pairs in proteins

A "working definition" for an ion-pair has been derived based upon analysis of the distance distributions for like- and oppositely charged groups in 38 proteins. Ion-pairs defined according to this criterion (less than or equal to 4 A between charged groups) have been analysed in respect of: (1) the frequencies of different pair types; (2) the residue separations and secondary structural locations of the residues involved; (3) the flexibility of the side-chains involved; (4) their conformation; (5) their environment (accessibility to solvent and proximity to active site or ligand binding regions); and (6) their conservation in related proteins. The results obtained indicate that on average one-third of the charged residues in a protein are involved in ion-pairs and 76% of these are concerned with stabilizing the tertiary (rather than the secondary) structure. Only 17% of ion-pairs are buried, and conservation of the interactions is generally low unless the residues involved have more specific functions to perform. In the light of the results obtained, the role of ion pairs in globular proteins is discussed.

Multiple internal reflectance infrared spectra of variably hydrated hemoglobin and myoglobin films: effects of globin hydration on ligand conformer dynamics and reactivity at the heme

Multiple internal reflectance infrared (IR) spectra are reported for variably hydrated films (1.2-0.1 g of H2O/g of protein) of the carbon monoxy and oxy forms of human Hb and sperm whale Mb. The spectra show that even the limited removal of liquid and icelike hydration constraints at the globin surface is sufficient to cause a dramatic, but completely reversible, shift toward a normally minute population of sterically unhindered, linear-perpendicular, Fe-CO conformer modes (nu CO = 1968-1967 cm-1), and the destabilization of distally hindered, tilted (or bent), Fe-CO modes (nu CO = 1951, 1944-1933 cm-1). Corroborative evidence from IR band broadening trends [delta delta nu 1/2 (1968, 1967 cm-1) approximately 2-4 cm-1], corresponding changes in the visible, and H-D exchange kinetics confirm that the shift toward 1968-1967 cm-1 results in a more open distal heme pocket configuration and that it is also accompanied by a buildup of deoxy-like steric hindrance proximal to the heme. Denaturation effects are eliminated as a potential cause of the shifts, as are specific protein-protein, ion-protein, intersubunit, and MIR crystal-film surface interactions. The hydration effect exhibits globin-dependent and ligand-dependent differences, which highlight the intrinsic importance of distal steric effects within the heme pocket and their dynamic coupling with exterior solvent constraints. CO-photodissociation and O2-exchange experiments conducted on rapidly interconverting (coupled and fully hydrated) and noninterconverting (uncoupled and partially hydrated) Fe-CO conformers also suggest that the open linear-perpendicular mode corresponds to a more tightly bound form of CO than the axially distorted Fe-CO species; similar differences are not evident in Fe-O2, which already prefers a bent end-on geometry within the heme pocket. Control IR spectra aimed at monitoring the progressive effects of various denaturants on HbCO further indicate that this same open mode serves as a common precursor to any of a number of more highly disordered folding modes. The overall properties of the 1968-1967-cm-1 conformer are discussed in terms of (1) the possibility of its corresponding to an available relaxation mode capable of facilitating the dynamics of ligand entry-release events and (2) its potential additional significance as a native folding mode that exhibits a marked tendency to be destabilized by hydration.

Dimeric hemoglobin of the bivalve mollusc Anadara broughtonii: complete amino acid sequence of the globin chain

The complete amino acid sequence of a dimeric hemoglobin (HbI) from the marine bivalve mollusc Anadara broughtonii was determined by sequencing of the intact chain and peptide fragments produced by cleavage at two asparaginylglycine bonds and at methionyl, arginyl, and tryptophanyl residues. The clam hemoglobin consists of two identical polypeptide chains. The globin chain has 146 amino acid residues with a proline at the NH2 terminus and a leucine at the COOH terminus. The calculated molecular mass of the native hemoglobin was 32945 daltons. The clam hemoglobin contains only two histidine residues, which correspond to the distal and proximal heme-linked positions. Compared with human beta chain, an additional segment of seven residues is present in the NH2-terminal region and also five less residues in the COOH-terminal region. Although such an amino-terminal elongation has been known to be characteristic of hemoglobins from the most primitive living vertebrates Cyclostomata, a very similar structure was found to occur in the hemoglobin from the primitive invertebrate arcid clam.

[Proteolytic degradation of native hemoglobin and its constituent parts--isolated subunits and globin. II. Correlation with the hydrogen exchange data and the mechanism of the burst-like proteolytic breakdown of native proteins]

Basing on comparison of the data on the rate of proteolytic breakdown and hydrogen exchange for hemoglobin and its constituent parts, we discuss the problem of the mechanism of the burst-like ("one-by-one") proteolytic breakdown of native proteins in conditions which are not close to extreme denaturational. The rate of proteolytic breakdown by different proteases decreases in the same order as the local conformational mobility according to the hydrogen exchange data: globin greater than oxy-alpha-chain greater than metHb much greater than oxy-beta-chain greater than HbO2 congruent to CNmetHb. For native globin and and metHb, the rates of hydrogen exchange and proteolytic breakdown depend weakly on the temperature in the range of 5-25 degrees, not much stronger than for flexible "unstructured" peptides and proteins. These correlations as well as other data allow a conclusion to be made that the process of the proteolytic breakdown of native proteins study is governed by spontaneous local conformational transitions of the same type as for the hydrogen exchange processes. A similar correlation between the changes in the rates of hydrogen exchange and proteolytic thought that the discussed mechanism of the burst-like proteolytic breakdown has a common character. Alongside with similarities, we consider distinctions between the role of the dynamical structure of the proteins in the realization of reactions of proteolytic degradation and the hydrogen exchange. Upon proteolytic degradation of stable native proteins, the significance of conformational rearrangement of the protein substrate induced by proteases and also that of distortions in the spatial structure of proteases under the action of the protein substrate increase. It is pointed that the actual concentration of the dynamic conformers of native proteins which serve as substrate for proteases can be much lower than the nominal concentration of the protein substrate. The mechanisms of the influence of the cofactor splitting and the dissociation of the oligomeric structure on the rate of proteolytic degradation are discussed.

[Proteolytic degradation of native hemoglobin and its constituent parts--isolated subunits and globin. I. Kinetic data and the character of the process of the breakdown of native forms]

The rates of proteolytic breakdown for native human hemoglobin (Hb) in CNmet-and oxy-forms, for isolated native alpha- and beta-chains of human Hb with deprotected SH-groups and for apo-Hb--globin at constant temperature 20 degrees as well as for metHb and globin in the temperature range 4-25 degrees were studied. The proteolysis of oxy-forms of proteins was performed in the presence of CN- to prevent the appearance in solution of quickly splitted aqua and hydroxy met-forms. Pepsin (at pH 5.5), trypsin (at pH 7.0 and 8.5) and protease VI (pronase) (at pH 7.0 and 8.5) were used as proteases. The rate of proteolysis was registered simultaneously by proteolysate precipitation in concentrated salt solutions (to determine the content of the native form), by precipitation in aqueous solution of trichloroacetic or perchloric acid and by colouring the terminal NH2-groups by ninhidrin in the total proteolysate. For most cases the data of all the three independent methods fell on a single kinetic curve, each pair protein--protease being represented by their individual curves. Therefore the breakdown of all the protein studied possesses a burst-like ("one-by-one", "all-or-none") character. The protein resistance to the attack by proteolytic enzymes increases in the following order: globin less than oxy-alpha-chain less than metHb less than oxy-beta-chain less than HbO2 congruent to CNmetHb. The use of control repeated proteolysis has made it possible to prove that differences in the rate of proteolytic degradation are not the consequence of spontaneous denaturation of the least unstable forms of proteins in the course of proteolytic reaction but are predetermined by the conformational state of the native macromolecule.

[The primary structure of the hemoglobin from a white rhinoceros (Ceratotherium simum, perissodactyla): beta 2 Glu]

The hemoglobin from a white rhinoceros (Ceratotherium simum) was analysed and the complete primary structure of the alpha and beta chains is described. The globin chains were separated on CM-cellulose column in 8M urea buffer. The amino acid sequences were mainly determined by automatic degradation of tryptic peptides in the sequenator. The results show, that globin consists of one alpha- and several beta-chain types. The beta chains differ at position beta 62 where the amino acids threonine, serine and alanine were identified and at position beta 116 where glutamine or lysine were found. The sequences are compared with those of horse, wild ass and zebra hemoglobin. Five amino acid residues of horse hemoglobin, which are involved in the alpha 1 beta 1 contacts are substituted in white rhinoceros hemoglobin. These substitutions are alpha 35 Gly leads to Ser, alpha 107 Ser leads to Val, alpha 111 Val leads to Leu, alpha 115 Asn leads to Gln and beta 116 Arg leads to Gln or Lys. Furthermore glutamic acid was found at position beta 2 of rhinoceros hemoglobin. In most mammalian hemoglobins the amino acid at this position is histidin which is one of the residues that binds, 2,3-bisphosphoglycerat in deoxyhemoglobin. In this way 2,3-bisphosphoglycerat controls the oxygen affinity of hemoglobin.

Protease and protease inhibitory activity in pregnant and postpartum involuting uterus

The presence of two distinct proteolytic activities in the rat uterus was confirmed with 14C-labeled globin used as a sensitive protein substrate and following release of label into the trichloroacetic acid-soluble supernatant fraction. Protease I is a cytoplasmic acid protease while protease II is associated with the pellet fraction, can be extracted by 0.6 M sodium chloride, and is active at pH 7.0. Protease I activity is low during pregnancy and markedly increases at term achieving maximal activity at day 3 post partum with a subsequent decline to preterm activity values. Lactation did not affect the uterine protease I activity. Protease II activity is not significantly different during pregnancy, at term, and post partum. The presence of an inhibitor of protease I was suggested by a decrease in enzyme activity with an increased cytosolic protein concentration. The inhibitor also lessened bovine trypsin activity but had no effect on protease II. Although its inhibitory potency on trypsin fluctuated during the various uterine physiologic stages, these changes appeared to be statistically insignificant. Human uterine samples were also found to contain the two protease activities with similar changes in protease I post partum. It is suggested that, both in the rat and in man, uterine involution post partum is associated with a marked increase in activity of acid cytosolic protease, while a particulate neutral protease and a soluble inhibitor of trypsin, which are also present in uterine cells, do not appear to play a significant role in the dissolution of uterine tissues after parturition.

Studies on Scapharca hemoglobins. Properties of the dimeric protein reconstituted with Fe- or Co-porphyrin

A native globin from the dimeric hemoglobin, hemoglobin I, of the mollusc Scapharca inaequivalvis has been obtained with the acid-acetone method. The globin has a lower sedimentation coefficient than the native protein at neutral pH; its reconstitution product with natural heme has the same physicochemical and functional properties as the native protein. proto- and meso-cobalt hemoglobin I have been prepared and characterized. proto-Cobalt hemoglobin I binds oxygen reversibly with a lower affinity and a lower cooperativity than native hemoglobin I; thus, the changes in the functional properties brought about by substitution of iron with cobalt are similar to those observed in human hemoglobin A. The EPR spectra of deoxy-proto-cobalt hemoglobin I and of the photolysis product of oxy-meso-cobalt hemoglobin I indicate that two histidine residues are the apical heme ligands. The broad signal at g = 2.38 in deoxy-proto-cobalt hemoglobin I points to a constrained structure of the heme site in this derivative which results from a distorted coordination of the hindered proximal histidine. A similar structure has been proposed previously for the alpha chains in deoxy-cobalt hemoglobin A.

The interaction of hemoglobin with phosphatidylserine vesicles

The interaction of hemoglobin with phosphatidylserine vesicles at low ionic strength and pH conditions was studied. The fluorescence intensity of a lipid embedded probe was quenched by bound Hb but could not be reversed by an elevation of ionic strength and pH. The irreversibility of the fluorescence quenching is a time-dependent process associated with changes in the heme Soret and visible spectra. The rate of these changes was much faster for methemoglobin than for either cyanomethemoglobin or oxyhemoglobin. Elevation of ionic strength released out of the bound hemoglobin into the water phase most of the globin but only a small fraction of the heme. The data are interpreted as demonstrating the ability of phosphatidylserine vesicles to compete with globin for the heme group. When Hb binds to the liposome, heme is being transferred into the lipid phase and the rate-limiting step is the dissociation of the heme-globin complex. The fact that binding of heme to the lipid vesicles is very strong was demonstrated by the failure of hemin to interact with globin when the two were rapidly mixed in the presence of phosphatidylserine vesicles. A multi-step process is suggested to explain the results of Hb phosphatidylserine interaction.

Amino acid sequences of the epsilon and alpha E globins of HbE, a minor early embryonic hemoglobin of the chicken

We have determined amino acid sequences for the alpha-like and beta-like globin components of HbE, one of the two minor hemoglobins in early chick embryos. The complete primary structure of the epsilon chain differs at 18 positions from the adult chicken beta globin, but there are no changes in heme-binding residues, alpha 1 beta 2 contact positions, or allosteric regulatory sites. By amino acid sequence analysis, we have identified a new alpha-like globin that we have called alpha E. The alpha E globin chain differs from the major adult alpha A chain at 22 amino acid positions. This paper discusses the structural and implied functional characteristics of these globins and presents hypotheses regarding the possible role of minor embryonic hemoglobins.

Evidence for the involvement of influenza A (fowl plague Rostock) virus protein P2 in ApG and mRNA primed in vitro RNA synthesis

Eleven temperature-sensitive (ts) mutants of influenza A (fowl plague, Rostock) virus were analysed for in vitro RNA transcriptase activity in reactions primed by ApG or globin mRNA at 31 degrees C or at 40.5 degrees C, the restrictive temperature for ts mutant growth. Only those ts mutants studied which were defective in RNA segment 1, coding for the virion P2 protein, were defective in RNA transcriptase activity when compared to wild-type virus. Mutants having a defect in the P2 protein had no significant RNA transcriptase activity in reactions at 40.5 degrees C primed by globin mRNA. However, one mutant showed RNA transcriptase activity similar to wild-type virus at 40.5 degrees C when ApG (0.3 mM) was used as primer. The results suggest that influenza (fowl plague, Rostock) P2 protein is directly involved in the mRNA priming reaction, as well as in the RNA transcription reaction in vitro.