The Hemoglobins

Interaction of ApoMyoglobin with Heme-hIAPP complex

Human Islet Amyloid Polypeptide (hIAPP) or amylin, can bind heme and the resultant complexes are prone to generate partially reduced oxygen species (PROS). The formation of PROS and the related oxidative stress highlight the importance of Heme-hIAPP in the onset and development of Type 2 Diabetes mellitus (T2Dm) in humans. In this study, the interaction of Heme-hIAPP with apomyoglobin (ApoMb) has been investigated using a combination of spectroscopic and electrophoresis techniques. Absorption, resonance Raman data and gel electrophoresis results confirm that ApoMb can uptake heme from Heme-hIAPP and constitute a six-coordinate high-spin ferric heme active site identical to that of myoglobin (Mb). The heme transfer reaction has two distinct kinetic steps. A possible mechanism of this reaction involves heme transfer to the apoprotein in the first step followed by a reorganisation of the protein chain to form the active site of native Mb. Increase in the pH of the reaction medium enhances the rate of the second step of heme transfer. This possibly corresponds to the deprotonation of a propionate side chain of the heme moiety at high pH which facilitates secondary interactions with the conserved distal Lys45 residue of horse heart Mb. Additionally, ApoMb sequesters ligand bound heme from Heme-hIAPP. After the heme transfer reaction, the amount of PROS formed by Heme-hIAPP complex diminishes significantly. This not only potentially diminishes heme-induced toxicity in the pancreatic β-cells but also produces Mb which has well-documented functions throughout the respiratory system and can thereby likely reduce the risks associated with T2Dm.

Electrophile tocopheryl quinones in apoptosis and mutagenesis: Thermochemolysis of thiol adducts with proteins and in cells

Electrophile tocopheryl quinones from the phenolic antioxidants gamma-tocopherol and delta-tocopherol form Michael adducts with the thiol nucleophile glutathione. These tocopheryl quinones are involved in cytotoxicity, apoptosis, and mutagenesis, and their biologic properties are associated with the depletion of intracellular thiols. We now show that both proteins and tissues treated with the electrophile gamma-tocopheryl quinone (gamma-TQ) form thiol adducts. The monoglutathion-S-yl derivative of gamma-TQ was subjected to thermochemolysis with the strong methylating base tetramethylammonium hydroxide. GC/MS showed four signature peaks and a fragmentation pattern characteristic of the thiol adduct. Similarly, pure monoglutathion-S-yl and diglutathion-S-yl derivatives of delta-TQ were subjected to thermochemolysis, and GC/MS showed characteristic fragmentation patterns for thiol adducts. The four signature peaks were identified when pure proteins with accessible thiol groups (hemoglobin and histone), FBS, and tissue culture medium and cell preparations were treated with gamma-TQ. Signature peaks in both complete medium and washed cells showed the presence of both soluble and insoluble thiol adducts. The effective or free arylating electrophile concentration in complete medium should always be evaluated in tissue culture studies. gamma-TQ is a mutagen but not a genotoxin; therefore, the histone adduct may be a previously unrecognized histone modification involved in chromatin dynamics leading to mutagenesis.

Conformational properties of the isolated 1-23 fragment of human hemoglobin alpha-chain

With the purpose of establishing whether, as a general rule, regions of a protein chain that are helical in the native structure maintain, at least partially, the same helical structure when isolated in solution, we have prepared the 1-23 fragment of human hemoglobin alpha-chain, and studied its conformational properties in aqueous solution by CD and 1H-NMR. From the analysis of CD and NMR spectral changes with temperature, salt and addition of trifluoroethanol (TFE) it can be concluded that the 1-23 peptide forms a measurable population (18% at 22 degrees C (pH 5.6) TFE/H2O, 30:70 (v/v)) of an alpha-helix structure that spans the same residues that are helical in the native protein (namely, 6 to 17). These results, taken together with similar ones obtained previously in the 1-19, 21-42 and 50-61 RNAase fragments, support the idea that no helices other than the native ones are actually formed in solution by protein fragments. This implies that the final helical structure of a protein is present from the very beginning of the folding process, and also that such elements of secondary structure can act as primary nucleation centers.

Subunit dissociation and activation of wild-type and mutant glucocorticoid receptors

Apparent molecular weights of wild-type and nti ('increased nuclear transfer') mutant glucocorticoid receptors were obtained from Stokes radii and sedimentation coefficients. At low salt concentrations molecular forms of Mr 328,000 and 298,000 of the wild-type and mutant, respectively, were predominant. Increasing ionic strength resulted in receptor dissociation. Dissociated forms of Mr 130,000 and 63,000 of the wild-type and mutant, respectively, were obtained at 300 mM KCl and above. Some metal oxi-anions prevented dissociation. Receptor activation to allow DNA binding produced the dissociated forms which could be separated from non-activated receptors by filtration through DNA-cellulose or by DEAE-cellulose chromatography. Non-activated wild-type and nti receptors eluted from DEAE-cellulose under identical conditions while activated wild-type and nti receptors eluted differently. Partially proteolyzed wild-type receptors behaved identically to nti receptors. We conclude that the large forms of wild-type and nti receptors are heteromeric and contain only one hormone-building polypeptide per complex.

Interaction of hemoglobin with band 3: a review

The oxygen transport protein hemoglobin interacts specifically and reversibly with the red cell membrane. pH and ionic strength dependence of these interactions indicate their electrostatic nature. The anion transport protein band 3 has been implicated as the protein to which hemoglobin binds. Hemoglobin, aldolase and glyceraldehyde 3-phosphate dehydrogenase have a similar pH and ionic strength dependence in binding to 23K fragment. The three compete for the same amino-terminal 23 residue sequence region of band 3. The binding site is a highly acidic segment without any positive charge. We have recently determined the sequence of amino-terminal 23K fragment of band 3. There is a remarkable internal sequence homology between the first eleven and next eleven residues in this sequence region. Biophysical measurements in this sequence region. Biophysical measurements have revealed that 23K is a tetramer under physiological conditions. The implications of this structure of 23K is discussed with respect to the interaction of band 3 with the red cell cytoskeleton.

Genetic determination of antibody specificity. Gene translocation and fusion, the molecular basis for the differentiation of the antibody-producing cell

The best system for the study of cell differentiation is a cell which in its differentiated state differs only by one product. This is the case in the immune system. The undifferentiated, but omnipotent stem cell differentiates into a committed B cell which produces only one type of specific antibody out of a million different, genetically fixed possibilities. Gene translocation and fusion is the basis of this differentiation process.

The deoxyribonucleic acid polymerases from the diatom Cylindrotheca fusiformis. Subcellular distribution, exonuclease activity and heterogeneity of the enzymes

Four DNA polymerases from the marine diatom Cylindrotheca fusiformis, polymerases A, B, C and D, were further differentiated by their subcellular localization, presence of deoxyribonuclease activity, apparent heterogeneity and molecular weights. Polymerases A, B and D occur in significant amounts in the soluble fraction, suggesting that they were originally localized in the nuclei, whereas polymerase C predominates in the chloroplasts. A mitochondrial DNA polymerase was also isolated and characterized by ion-exchange chromatography. Polymerase D has an associated nuclease activity which prefers denatured DNA and Mg2+, and has a pH optimum higher than that for polymerase activity. Co-elution from a DEAE-Sephadex column and co-sedimentation in glycerol density gradients of deoxyribonuclease and polymerase D activity suggest a molecular association. Polymerases A, B and C are devoid of nuclease activity. Glycerol-gradient-sedimentation analysis showed that all DNA polymerase fractions are heterogeneous at low ionic strengths, with the appearance of a single homogeneous activity of 0.5M-KCl. Estimated molecular weights of 100000, 82000 and 120000 for polymerases A, B and C respectively were obtained from sedimentation analysis and gel filtration. Polymerase D was estimated to have a molecular weight of about 100000 as determined by sedimentation analysis alone.

Sheep prothrombin: purification and partial characterization

A procedure for the preparation of highly purified sheep prothrombin is described. The purified zymogen, when subjected to disc gel electrophoresis in polyacrylamide, gave rise to one single band. Only alanine was found as N-terminal residue. Carboxypeptidases A and B failed to release any C-terminal residue. The isoelectric point, as determined by isoelectric focusing in polyacrylamide gel slab, was shown to be 4.9-5.0. Non-chromatographed, but not the purified zymogen, could be converted into active thrombin in half-saturated trisodium citrate seeded with thrombin. Pure sheep prothrombin showed 5.6% of neutral sugars and the following amino acid composition: Ala35, Arg44, Asx54-55, -Cys24, Glx72, Gly53-54, His8, Ile19, Leu45, Lys31, Met7, Phe23, Pro36, Ser34, Thr29-29, Trp16, Tyr19 and Val33, which accounts for a molecular weight of about 66 000 (amino acids only). The molecular weight as determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis after reduction by 2-mercaptoethanol, was shown to be 77 000 +/- 3000 (carbohydrates included).

Protein incorporation by isolated amphibian oocytes. V. Specificity for vitellogenin incorporation

Macromolecules of vitellogenin were sequestered by Xenopus laevis oocytes 20-50 times (on a molar basis) more rapidly than other proteins tested. Selectivity for vitellogenin did not appear to involve molecular size or charge. The Km for vitellogenin incorporation was at least several orders of magnitude less than that for bovine serum albumin (BSA). At concentrations less than 10 mg-ml-1, BSA did not measurably compete with vitellogenin; a slight, apparent competition observed above a BSA concentration of 10 mg-ml-1 was probably spurious. Above a concentration of 2 mg-ml-1, vitellogenin promoted BSA incorporation by about 40%. These results are consistent with the notion that vitellogenin binds to specific receptor sites on the oocyte membrane and is subsequently internalized by micropinocytosis. Other proteins, such as BSA, which do not compete with vitellogenin are most likely to be incorporated by adventitious engulfment during micropinocytosis.

An extracellular aminopeptidase from Clostridium histolyticum

An aminopeptidase was isolated from the culture filtrate of Clostridium histolyticum and purified to homogeneity. Absence of endopeptidase activity in the purified preparation was demonstrated. Gel filtration on a calibrated column indicates an apparent molecular weight of 340000 for the native enzyme. Gel electrophoresis of the denatured enzyme in the presence of dodecylsulfate in constant acrylamide concentration and in a concentration gradient, resulted in the appearance of a single component for which a molecular weight of 51000 and 59000 respectively, was calculated. From mobilities of crosslinked and denatured protein species a molecular weight of 56000 was obtained for the monomer. Specificity studies show that the enzyme cleaves all types of N-terminel amino acid residues including proline and hydroxyproline from small peptides and from polypeptides. The peptide bond formed between an N-terminal amino acid residue and proline is not cleaved by the enzyme. The combined action of aminopeptidase-P and clostridal aminopeptidase leads to complete hydrolysis of the proline-rich nonapeptide bradykinin. Low rates of hydrolysis was observed for charged residues, and amides of amino acids. Kinetic studies with five tripeptides of the general structure X-Gly-Gly, where X stands for Leu, Phe, Val, Ala, or Pro, show a decrease in Km with the increasing size of the hydrophobic side chain of X. The highest Kcat values are observed with proline and alanine. In the series Pro-Gly, Pro-Gly-Pro, Pro-Gly-Pro-Pro, the last peptide is the best substrate, indicating an active site complementary to at least four amino acid residues. The enzymatic activity is dependent on the presence of divalent cations, maximal activation being reached with Mn2+ and Co2+. The optimal pH for the Mn2+ and Co2+- activated enzyme is 8.6 and 8.2 respectively. The optimal temperature is 40 degrees C. Inhibition of the aminopeptidase was achieved with Zn2+, Cu2+ and p-mercuribenzoate, but not with diisopropylphosphofluoridate.

Synthesis of the myoglobin active site

A simple heme-imidazole compound, having the same geometry as the heme-imidazole complex in myoglobin, has been synthesized. This compound, ferropyrroporphyrin-N-[3-(1-imidazolyl)propyl]amide, reversibly binds oxygen in the solid state or when dissolved in a polystyrene film. These results suggest that the principal factors governing reversible oxygen binding are the electronic nature of the base (imidazole), neighboring-group effects of the basic group, and immobilization of the heme group.