Additional Positive Charge Research Articles

Conopressin-T from Conus tulipa Reveals an Antagonist Switch in Vasopressin-like Peptides

We report the discovery of conopressin-T, a novel bioactive peptide isolated from Conus tulipa venom. Conopressin-T belongs to the vasopressin-like peptide family and displays high sequence homology to the mammalian hormone oxytocin (OT) and to vasotocin, the endogenous vasopressin analogue found in teleost fish, the cone snail's prey. Conopressin-T was found to act as a selective antagonist at the human V 1a receptor. All peptides in this family contain two conserved amino acids within the exocyclic tripeptide (Pro7 and Gly9), which are replaced with Leu7 and Val9 in conopressin-T. Whereas conopressin-T binds only to OT and V 1a receptors, an L7P analogue had increased affinity for the V 1a receptor and weak V2 receptor binding. Surprisingly, replacing Gly9 with Val9 in OT and vasopressin revealed that this position can function as an agonist/antagonist switch at the V 1a receptor. NMR structures of both conopressin-T and L7P analogue revealed a marked difference in the orientation of the exocyclic tripeptide that may serve as templates for the design of novel ligands with enhanced affinity for the V 1a receptor.

The Serine Protease Domain of Hepatitis C Viral NS3 Activates RNA Helicase Activity by Promoting the Binding of RNA Substrate

Nonstructural (NS) protein 3 is a DEXH/D-box motor protein that is an essential component of the hepatitis C viral (HCV) replicative complex. The full-length NS3 protein contains two functional modules, both of which are essential in the life cycle of HCV: a serine protease domain at the N terminus and an ATPase/helicase domain (NS3hel) at the C terminus. Truncated NS3hel constructs have been studied extensively; the ATPase, nucleic acid binding, and helicase activities have been examined and NS3hel has been used as a target in the development of antivirals. However, a comprehensive comparison of NS3 and NS3hel activities has not been performed, so it remains unclear whether the protease domain plays a vital role in NS3 helicase function. Given that many DEXH/D-box proteins are activated upon interaction with cofactor proteins, it is important to establish if the protease domain acts as the cofactor for stimulating NS3 helicase function. Here we show that the protease domain greatly enhances both the direct and functional binding of RNA to NS3. Whereas electrostatics plays an important role in this process, there is a specific allosteric contribution from the interaction interface between NS3hel and the protease domain. Most importantly, we establish that the protease domain is required for RNA unwinding by NS3. Our results suggest that, in addition to its role in cleavage of host and viral proteins, the NS3 protease domain is essential for the process of viral RNA replication and, given its electrostatic contribution to RNA binding, it may also assist in packaging of the viral RNA.

Molecular mechanisms of fibrillogenesis and the protective role of amyloid P component: two possible avenues for therapy.

Amyloid deposits regress when the supply of fibril precursor proteins is sufficiently reduced, indicating that amyloid fibrils are degradable in vivo. Serum amyloid P component (SAP), a universal constituent of amyloid deposits, efficiently protects amyloid fibrils from proteolysis in vitro, and may contribute to persistence of amyloid in vivo. Drugs that prevent binding of SAP to amyloid fibrils in vivo should therefore promote regression of amyloid and we are actively seeking such agents. A complementary strategy is identification of critical molecular processes in fibrillogenesis as targets for pharmacological intervention. All amyloidogenic variants of apolipoprotein AI contain an additional positive charge in the N-terminal fibrillogenic region of the protein. This is unlikely to be a coincidence and should be informative about amyloidogenesis by this protein. The two amyloidogenic variants of human lysozyme, caused by the first natural mutations found in its gene, provide a particularly powerful model system because both the crystal structure and folding pathways of wild-type lysozyme are so well characterized. The amyloidogenic variant lysozymes have similar 3D crystal structures to the wild type, but are notably less thermostable. They unfold on heating, lose enzymic activity, and aggregate to form amyloid fibrils in vitro.

α‐Conotoxin analogs with additional positive charge show increased selectivity towards Torpedo californica and some neuronal subtypes of nicotinic acetylcholine receptors

Alpha-conotoxins from Conus snails are indispensable tools for distinguishing various subtypes of nicotinic acetylcholine receptors (nAChRs), and synthesis of alpha-conotoxin analogs may yield novel antagonists of higher potency and selectivity. We incorporated additional positive charges into alpha-conotoxins and analyzed their binding to nAChRs. Introduction of Arg or Lys residues instead of Ser12 in alpha-conotoxins GI and SI, or D12K substitution in alpha-conotoxin SIA increased the affinity for both the high- and low-affinity sites in membrane-bound Torpedo californica nAChR. The effect was most pronounced for [D12K]SIA with 30- and 200-fold enhancement for the respective sites, resulting in the most potent alpha-conotoxin blocker of the Torpedo nAChR among those tested. Similarly, D14K substitution in alpha-conotoxin [A10L]PnIA, a blocker of neuronal alpha7 nAChR, was previously shown to increase the affinity for this receptor and endowed [A10L,D14K]PnIA with the capacity to distinguish between acetylcholine-binding proteins from the mollusks Lymnaea stagnalis and Aplysia californica. We found that [A10L,D14K]PnIA also distinguishes two alpha7-like anion-selective nAChR subtypes present on identified neurons of L. stagnalis: [D14K] mutation affected only slightly the potency of [A10L]PnIA to block nAChRs on neurons with low sensitivity to alpha-conotoxin ImI, but gave a 50-fold enhancement of blocking activity in cells with high sensitivity to ImI. Therefore, the introduction of an additional positive charge in the C-terminus of alpha-conotoxins targeting some muscle or neuronal nAChRs made them more discriminative towards the respective nAChR subtypes. In the case of muscle-type alpha-conotoxin [D12K]SIA, the contribution of the Lys12 positive charge to enhanced affinity towards Torpedo nAChR was rationalized with the aid of computer modeling.

Charge centers inCaF2:Ab initiocalculation of elementary physical properties

Charge centers in ionic crystals provide a channel for elementary interaction between electromagnetic radiation and the lattice. We calculate the electronic ground state energies which are needed to create a charge center -- namely a $F$- and a $H$-center. In well agreement with common understanding the $F$-center results in being accompanied by a small lattice distortion whereas the $H$-center is accompanied by a very large lattice deformation. Opposite to the common understanding the additional positive charge in the charge center results rather to be localized on a F$_4^{3-}$ complex than on a F$_2^-$-complex. From the ground states of the charge centers we derive binding energies, diffusion barriers and agglomeration energies for $M$-center formation. These microscopic quantities are of fundamental interest to understand the dynamic processes which are initiated if the crystals interact with extreme intense deep ultra violet radiation. We further derive the equilibrium concentrations of charge centers in grown crystals.

Protonation of carboxyl latex particles in the presence of a strong cationic polyelectrolyte

The charging behavior of carboxyl latex surface in the presence of poly(diallyl dimethyl ammonium chloride) (DADMAC) was investigated by means of potentiometric titrations and electrophoretic mobility. The titration curves at different ionic strengths show a common crossing point, which coincides with the point of zero mobility, and can be identified with the point of zero charge (PZC). This characteristic behavior is due to the adsorption of the strong cationic polyelectrolyte on the weak acid particle surface, leading to an additional positive charge, and a corresponding shift of the surface potential. These features can be quantified in terms of modified Stern model and the standard electrokinetic model. This model predicts the PZC very well, while the magnitude of the charge and its ionic strength dependence are reproduced only semi-quantitatively.

Alteration of Rb binding to HPV 18 E7 modified by transglutaminase 2 with different type of polyamines

High-risk human papillomavirus (HPV) E7 is a major oncoprotein that plays a crucial role in the development of cervical cancer. A previous study showed that transglutaminase (TGase) 2 catalyzes the incorporation of polyamines into HPV 18 E7 protein, and thereby diminishes its ability to bind Rb. Therefore, TGase 2 activity may be implicated in a suppressive function of host against HPV-induced carcinogenesis. To better understand the nature of polyamination of HPV 18 E7, we investigated the Rb binding of E7 polyaminated in vitro with different type of polyamines. The incorporation of spermine diminished the Rb binding of E7 more profoundly compared with that of spermidine, suggesting that either the additional positive charge or a steric effect or both may have altered the chemical or structural properties of the protein. In addition, the treatment of either spermidine or spermine in cultured cell system reduced the ability of E7 to inactivate Rb with a TGase activity-dependent manner. Spermine was more effective in inhibiting E7 activity than spermidine. These results may provide the basis for future investigation aiming at delineating the significance of polyamine metabolism on HPV E7 functions.

Analysis of the Contribution of Individual Substituents in 4,6-Aminoglycoside-Ribosome Interaction

The 4,6-disubstituted 2-deoxystreptamines interfere with protein biosynthesis by specifically targeting the ribosomal A site. These drugs show subtle variations in the chemical groups of rings I, II, and III. In the present study we used site-directed mutagenesis to generate mutant strains of Mycobacterium smegmatis mc(2)155 SMR5 DeltarrnB with mutations in its single rRNA allele, rrnA. This genetic procedure gives rise to strains carrying homogeneous populations of mutant ribosomes and was used to study the contribution of individual chemical substituents to the binding of 4,6-disubstituted aminoglycosides. X-ray crystal structures of geneticin and tobramycin complexed to oligonucleotides containing the minimal bacterial ribosomal A site were used for interpretation of MICs determined for a panel of 4,6-aminoglycosides, including tobramycin, kanamycin A, kanamycin B, amikacin, gentamicin, and geneticin. Surprisingly, the considerable differences present within ring III did not seem to alter the interaction of the drug with the ribosome, as determined by site-directed mutagenesis of the A site. In contrast, subtle variations in ring I significantly influenced binding: (i) a 4'-hydroxyl moiety participates in the proper drug target interaction; and (ii) a 2'-amino group contributes an additional positive charge to ring I, making the drug less susceptible to any kind of sequence alteration within the decoding site, most notably, to conformational changes induced by transversion of U1495 to 1495A. The 4-amino-2-hydroxyl-1-oxobutyl extension at position 1 of ring II of amikacin provides an additional anchor and renders amikacin less dependent on the structural conformation of nucleotide U1406 compared to the dependencies of other kanamycins. Overall, the set of interactions forming the complex between drug substituents and nucleotides of the A site constitutes a network in which the interactions can partly compensate for each other when they are disrupted.

Engineering and impact of surface states on AlGaN/GaN-based hetero field effect transistors

This work investigates the impact and origin as well as the electrical behaviour of surface states of AlGaN/GaN-based heterostructure field effect transistors (HFETs). Different GaN-cap layers were grown on top of AlGaN-barrier layers, and the active transistor surface areas were treated chemically differently. The investigations show that one relevant surface state at the AlGaN/GaN surface is that of donor-like N-vacancies. Surface plasma treatments with O2- and N2-plasmas on structures with and without GaN-cap layers reveal very different electrical dc behaviour of AlGaN/GaN-based HFETs. Band structure simulations and considerations explain the different character of surface states and the impact on the dc channel current as well as the influence on threshold voltage and barrier height by Fermi-level pinning. N-vacancies on the surface of AlGaN/GaN HFETs are ionized and therefore very sensitive to N2-treatment, whereas on GaN/AlGaN/GaN surfaces they remain neutral and do not affect nS and ID significantly. Oxidation, however, also introduces acceptor-like surface states, which become ionized only in the case of GaN capping, leading to an additional positive charge at the upper heterojunction and increasing negative charge in the channel. It is further shown that 30 nm low-temperature grown GaN capping drastically reduces the gate leakage, leading to a transistor with insulated gate characteristics.

Assignment of voltage-gated potassium channel blocking activity to κ-KTx1.3, a non-toxic homologue of κ-hefutoxin-1, from Heterometrus spinifer venom

A new family of weak K + channel toxins (designated κ-KTx) with a novel “bi-helical” scaffold has recently been characterized from Heterometrus fulvipes (Scorpionidae) venom. Based on the presence of the minimum functional dyad (Y5 and K19), κ-hefutoxin-1 (κ-KTx1.1) was investigated and found to block Kv 1.2 (IC 50 ∼40 μM) and Kv 1.3 (IC 50 ∼150 μM) channels. In the present study, κ-KTx1.3, that shares ∼60% identity with κ-hefutoxin 1, has been isolated from Heterometrus spinifer venom. Interestingly, despite the presence of the functional dyad (Y5 and K19), κ-KTx1.3 failed to reproduce the K + channel blocking activity of κ-hefutoxin-1. Since the dyad lysine in κ-KTx1.3 was flanked by another lysine (K20), it was hypothesized that this additional positive charge could hinder the critical electrostatic interactions known to occur between the dyad lysine and the Kv 1 channel selectivity filter. Hence, mutants of κ-KTx1.3, substituting K20 with a neutral (K20A) or a negatively (K20E) or another positively (K20R) charged amino acid were synthesized. κ-KTx1.3 K20E, in congruence with κ-hefutoxin 1 with respect to subtype selectivity and affinity, produced blockade of Kv 1.2 (IC 50 = 36.8 ± 4.9 μM) and Kv 1.3 (IC 50 = 53.7 ± 6.7 μM) but not Kv 1.1 channels. κ-KTx1.3 K20A produced blockade of both Kv 1.2 (IC 50 = 36.9 ± 4.9 μM) and Kv 1.3 (IC 50 = 115.7 ± 7.3 μM) and in addition, acquired affinity for Kv 1.1 channels (IC 50 = 110.7 ± 7.7 μM). κ-KTx1.3 K20R failed to produce any blockade on the channel subtypes tested. These data suggest that the presence of an additional charged residue in a position adjacent to the dyad lysine impedes the functional block of Kv 1 channels produced by κ-KTx1.3.

P-type one-sided hexagonal spiral drift detectors

A new P-type drift detector (PDD) with one-sided hexagonal spiral shaped cathodes around the center anode has been designed, simulated, constructed and tested. The signal in PDD is generated by the transport of holes (instead of electrons as in an n-type drift detector) in the bulk of the detector and their arrival to the anode. Large arrays of drift cells are required for the extended X-ray absorption fine structure experiments (EXAFS). The large number of cells forces the design of the drift cell with a minimal number of bonds per cell. The presented design creates the drift field by the spiral-based voltage divider. Moreover, the leakage current created at the depleted part of the detector surface is also collected without an external connection to the cell. The leakage current is collected directly on the inner terminal of the divider. The lithographic processes of the wafer are done only on one side resulting in a much faster fabrication. The lithography-less side of the detector was uniformly implanted with phosphorus creating a shallow, rectifying p/sup -/n/sup +/ junction. This side is exposed to the radiation. Positive charges in the native oxide help to keep the thickness of the dead entrance layer at the minimum. Moreover, this layer is not sensitive to the radiation damage caused by very low energy X-rays that do not damage the silicon structure and produce only additional positive charge in the oxide. For the first time, the design makes an active usage of the positive charge in the oxide as a rectifying junction on p-type silicon.

New Synthetic Approaches to Multifunctional Phenazinium Salt Derivatives

Two different approaches are offered for the synthesis under mild conditions of disubstituted phenazinium and benzo[a]phenazinium salts. Direct nucleophilic substitutions by primary and secondary amines in quaternary phenazinium salts containing an additional positive charge in the aliphatic part of the molecule were carried out. The substitution proceeds successively in positions 2 and 7, which allows selective introduction of different substituents into the heterocycle. Direct nucleophilic substitution in quaternary 2-N-alkyl-acetamidophenazinium and 5-alkoxy-benzo[a]phenazinium salts with different amines can also serve as a convenient method for the introduction of two different substituents.

The charge accumulation in an insulator and the states at interfaces of silicon-on-insulator structures as a result of irradiation with electrons and gamma-ray photons

The accumulation of charge in an insulator and the states at interfaces in silicon-on-insulator structures irradiated with 2.5-MeV electrons and 662-keV gamma-ray photons were studied. It was found that an additional positive charge appears in the buried insulator of the structures as a result of irradiation. The concentration of hole traps generated by radiation in the oxide is higher at the boundary with substrate than at the bonding interface between a split-off silicon layer and oxide. It is shown that the presence of even a weak built-in field in the structures (F≳5×103 V/cm) gives rise to efficient separation of charge carriers. There is no generation of additional states at the Si/SiO2 interfaces in the silicon-on-insulator structures for both irradiation types, although this generation is observed in the initial thermal oxide.

DFT study of the Jahn–Teller impurity Rh2+ in octahedral symmetry

AbstractDensity functional calculations on clusters involving up to 87 atoms have been carried out for exploring the Jahn–Teller effect in NaCl: Rh2+. Due to the flexibility of density functional theory (DFT) methodology, calculations have first been performed for a ground state described by the (3z2 − r2)0.5(x2 − y2)0.5 configuration at different values of the Qθ(≈3z2 − r2) distortion. This electronic configuration allows one to extract the angular frequency, ωE, and anharmonic parameter, A3, corresponding to a hypothetical Rh2+ ion without orbital degeneracy. The calculation on an 87‐atom cluster indicates that ligands have undergone a 10% inward relaxation whereas the first Na+ ions along <100> directions experience a small outward relaxation. The latter fact is related to the additional positive charge created through the Na+ → Rh2+ substitution. Calculations at different Qθ(≈3z2 − r2) distortions for a ground state described by (3z2 − r2)1 and (x2 − y2)1 configurations have also been carried out and reveal that: (1) the energy minimum for the former electronic configuration corresponds to an elongated octahedron lying ≈200 cm−1 below the minimum associated with (x2 − y2)1 configuration displaying a compressed D4h geometry; (2) the calculated ratio EJT/ℏωE where EJT is the Jahn–Teller energy is found to be equal to 7.5, stressing that the Jahn–Teller effect in NaCl: Rh2+ is strong. These conclusions concur with available experimental findings. The current calculations reasonably account for the two crystal‐field transitions and the charge transfer band detected through magnetic circular dichroism up to 4.1 eV. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 2003

Raman spectroscopy of the PTCDA–inorganic semiconductor interface: evidence for charge transfer

In the present work, we investigate the vibrational properties of a PTCDA molecule with an additional positive or negative charge using density functional theory. With respect to the calculated vibrational frequencies of the neutral molecule, some modes in particular in the region 1200–1800 cm −1 show large shifts. These calculations are compared with resonant Raman spectra of sub-monolayer PTCDA films on passivated semiconductor surfaces, both before and after annealing the deposited films at elevated temperatures (350 °C). Independent of the sample treatment, the sub-monolayer Raman spectra correspond quite well to reference spectra obtained for thicker films, and we find no evidence for the strong shifts predicted in the calculations for the charged species. From the small changes in the mode frequencies it can be concluded that any charge transfer present involves significantly less than one elementary charge.

Novel site in lipoprotein lipase (LPL415–438) essential for substrate interaction and dimer stability

LPL, like other lipases, has the ability to hydrolyze water-insoluble lipid substrates, but the mechanism is incompletely understood. We previously demonstrated a 22-amino acid loop in the amino-terminal domain of LPL to be essential for interaction with lipid substrates (Dugi, K. A., H. L. Dichek, G. D. Talley, H. B. Brewer, Jr., and S. Santamarina-Fojo. 1992. J. Biol. Chem. 267: 25086–25091) and mediation of substrate specificity (Dugi, K. A., H. L. Dichek, and S. Santamarina-Fojo. 1995. J. Biol. Chem. 270: 25396–25401). The carboxy-terminal domain, LPL415–438, contains two highly conserved hydrophobic stretches, and represents a candidate region for substrate interactions. Specific point mutations or deletion of the region between the hydrophobic stretches (LPL419–430) caused up to 90% selective loss of hydrolyzing activity against water-insoluble triolein, but not against water-soluble tributyrin, implicating a crucial function for LPL419–430 in the interaction with lipid substrates. In contrast, mutations introduced into the hydrophobic regions led to concomitant changes in tributyrin and triolein activities. The presence of an additional positive charge at position 416 yielded a gain of function mutant with 3-fold increased activity. This mutant was about three times more stable at 37°C than wild-type LPL, suggesting an important role for the hydrophobic regions in LPL dimer stability. In summary, our data demonstrate that the carboxy-terminal region LPL415–438 plays an important role in both the interaction of LPL with lipid substrates and the stability of the LPL homodimer. —Keiper, T., J. G. Schneider, and K. A. Dugi. Novel site in lipoprotein lipase (LPL415–438) essential for substrate interaction and dimer stability.

Structural characteristics of protein binding sites for calcium and lanthanide ions.

Surveys of X-ray structures of Ca2+-containing and lanthanide ion-containing proteins and coordination complexes have been performed and structural features of the metal binding sites compared. A total of 515 structures of Ca2+-containing proteins were considered, although the final data set contained only 44 structures and 60 Ca2+ binding sites with a total of 323 ligands. Eighteen protein structures containing lanthanide ions were considered with a final data set containing eight structures and 11 metal binding sites. Structural features analysed include coordination numbers of the metal ions, the identity of their ligands, the denticity of carboxylate ligands, and the type of secondary structure from which the ligands are derived. Three general types of calcium binding site were identified in the final data set: class I sites supply the Ca2+ ligands from a continuous short sequence of amino acids; class II sites have one ligand supplied by a part of the amino acid sequence far removed from the main binding sequence; and class III sites are created by amino acids remote from one another in the sequence. The abundant EF-hand type of Ca2+ binding site was under-represented in the data set of structures analysed as far as its biological distribution is concerned, but was adequately represented for the chemical survey undertaken. A turn or loop structure was found to provide the bulk of the ligands to Ca2+, but helix and sheet secondary structures are slightly better providers of bidentate carboxylate ligation than turn or loop structures. The average coordination number for Ca2+ was 6.0, though for EF-hand sites it is 7. The average coordination number of a lanthanide ion in an intrinsic protein Ca2+ site was 7.2, but for the adventitious sites was only 4.4. A survey of the Cambridge Structural Database showed there are small-molecule lanthanide complexes with low coordination numbers but it is likely that water molecules, which do not appear in the electron density maps, are present for some lanthanide sites in proteins. A detailed comparison of the well-defined Ca2+ and lanthanide ion binding sites suggests that a reduction of hydrogen bonding associated with the ligating residues of the binding sites containing lanthanide ions may be a response to the additional positive charge of the lanthanide ion. Major structural differences between Ca2+ binding sites with weak and strong binding affinities were not obvious, a consequence of long-range electrostatic interactions and metal ion-induced protein conformational changes modulating affinities.

Fabrication of Ca-doped large grain Y-Ba-Cu-O superconductors

Doping the rare earth site in superconducting YBa/sub 2/Cu/sub 3/O/sub x/, (Y-123) with Ca generates additional positive charge carrier density in the Cu-O planes and, at a certain hole concentration, enhances the critical current density and irreversibility field of the material. 3 cm sized large, single grain samples of YBCO doped with various amounts of Ca have been fabricated by a top seeded melt growth technique. Very fine, sub-micron sized secondary phase particles of Y-211, which enhance flux pinning, have been observed in the (Y,Ca)Ba/sub 2/Cu/sub 3/O/sub y/ matrix without the addition of Pt. It is considered that Ca doping within the Y-211 phase is responsible for the refinement of these particles. In this paper we discuss the effect of Ca doping on growth rate, microstructural features and superconducting properties of large YBCO pseudo-crystals.

Probing the diphosphoglycerate binding pocket of HbA and HbPresbyterian (beta 108Asn --> Lys).

HbPresbyterian (beta 108Asn --> Lys, HbP) contains an additional positive charge (per alpha beta dimer) in the middle of the central cavity and exhibits a lower oxygen affinity than wild-type HbA in the presence of chloride. However, very little is known about the molecular origins of its altered functional properties. In this study, we have focused on the beta beta cleft of the Hb tetramer. Recently, we developed an approach for quantifying the ligand binding affinity to the beta-end of the Hb central cavity using fluorescent analogues of the natural allosteric effector 2, 3-diphosphoglycerate (DPG) [Gottfried, D. S., et al. (1997) J. Biol. Chem. 272, 1571-1578]. Time-correlated single-photon counting fluorescence lifetime studies were used to assess the binding of pyrenetetrasulfonate to both HbA and HbP in the deoxy and CO ligation states under acidic and neutral pH conditions. Both the native and mutant proteins bind the probe at a weak binding site and a strong binding site; in all cases, the binding to HbP was stronger than to HbA. The most striking finding was that for HbA the binding affinity varies as follows: deoxy (pH 6.35) > deoxy (pH 7.20) > CO (pH 6.35); however, the binding to HbP is independent of ligation or pH. The mutant oxy protein also hydrolyzes p-nitrophenyl acetate, through a reversible acyl-imidazole pathway linked to the His residues of the beta beta cleft, at a considerably higher rate than does HbA. This implies a perturbation of the microenvironment of these residues at the DPG binding pocket. Structural consequences due to the presence of the new positive charge in the middle of the central cavity have been transmitted to the beta beta cleft of the protein, even in its liganded conformation. This is consistent with a newly described quaternary state (B) for liganded HbPresbyterian and an associated change in the allosteric control mechanism.

Reagents for specific modification of biopolymers

Direct nucleophilic substitution of primary and secondary amines for hydrogen in quaternary phenazinium salts containing an additional positive charge in the aliphatic part of the molecule was carried out. The substitution proceeds successively in positions 2 and 7, which allows selective introduction of different substituents into the heterocycle.