Biomedical subjects

S Nir

Publications and source records attributed to S Nir.

At least 37 records · Page 2Linked to original sources

PubMed1999

Interactions of influenza virus with cultured cells: detailed kinetic modeling of binding and endocytosis.

We performed a detailed kinetic analysis of the uptake of influenza virus (A/PR8/34) by Madin Darby canine kidney (MDCK) cells in culture. Experimental procedures were based on the relief of fluorescence self-quenching of the fluorescent probe octadecylrhodamine B chloride (R18) incorporated in the viral envelope. Equilibrium for binding of influenza virus to MDCK cells (2.5 x 10(6)/mL) was reached quicker with temperature increases due to a faster dynamic mobility of the particles. We deduced that there are two kinds of binding sites for influenza virus in MDCK cells and determined the kinetic parameters of the binding process (adhesion and detachment rate constants), using a mass action kinetic model. As the temperature increases, the number of binding sites for influenza virus decreases, especially the high-affinity binding sites, whereas the value of the affinity constant for virus binding to the binding site, k, increases. Nevertheless, the binding association constant at equilibrium Ki, which is given by Ki = Niki, where Ni is the number of binding sites per cell, declines as the temperature increases. When endocytosis occurs, the total uptake of virions by the cells is larger than that observed in the process of binding at the same temperature, and the uptake proceeds for longer times. Using our mass kinetic model, we determined that at 20 degrees C, the rate constant of endocytosis, epsilon, for influenza virus with this cell line is 2.6 x 10(-)4 s-1, i.e., in the same range as in studies on endocytosis of liposomes.

Animals↗

PubMed1999

Interactions of Monovalent Organic Cations with Pillared Clays.

Interactions between an acid-activated pillared clay and several organic cations including dyes (methylene blue, MB; crystal violet, CV; acriflavin, AF) and benzyl derivatives (benzyltrimethylammonium, BTMA; benzyltriethylammonium, BTEA) were studied by adsorption measurements and X-ray diffraction. When the dyes were adsorbed from low ionic strength solutions, adsorption was irreversible but saturated at levels below the cation exchange capacity (CEC) of the clay (0.6 meq/g). The difference with CEC value was largest for CV. This mode of adsorption was interpreted in terms of interlayer adsorption with steric hindrance in the pillared galleries. On the other hand, when the dyes were adsorbed from high ionic strength solutions, adsorption levels well beyond the CEC of the clay could be reached, in particular for MB and CV. This was interpreted in terms of a second adsorption mode, involving formation of molecular aggregates on the outer surface of the clay, as evidenced by X-ray diffraction. The behavior of the cationic benzyl derivatives was markedly different, with an adsorption level always below the CEC and a decrease of adsorption as the ionic strength was increased, as expected for non-complex-forming cations. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

Orientation of the pore-forming peptide GALA in POPC vesicles determined by a BODIPY-avidin/biotin binding assay.

We determined the orientation of a biotinylated version of the pore-forming peptide GALA (WEAALAEALAEALAEHLAEALAEALEALAA) at pH 5.0 in large unilamellar phosphatidylcholine vesicles, using the enhancement of BODIPY-avidin fluorescence subsequent to its irreversible binding to a biotin moiety. GALA and its variants were biotinylated at the N- or C-terminus. BODIPY-avidin was either added externally or was pre-encapsulated in vesicles to assess the fraction of liposome-bound biotinylated GALA that exposed its labeled terminus to the external or internal side of the bilayer, respectively. Under conditions where most of the membrane-bound peptides were involved in transmembrane aggregates and formed aqueous pores (at a lipid/bound peptide molar ratio of 2500/1), the head-to-tail (N- to C-terminus) orientation of the membrane-inserted peptides was such that 3/4 of the peptides exposed their N-terminus on the inside of the vesicle and their C-terminus on the outside. Under conditions resulting in reduced pore formation (at higher lipid/peptide molar ratios), we observed an increase in the fraction of GALA termini exposed to the outside of the vesicle. These results are consistent with a model (Parente et al., Biochemistry, 29:8720, 1990) that requires a critical number of peptides (M) in an aggregate to form a transbilayer structure. When the peptides form an aggregate of size i, with i < M = 4 to 6, the orientation of the peptides is mostly parallel to the membrane surface, such that both termini of the biotinylated peptide are exposed to external BODIPY-avidin. This BODIPY-avidin/biotin binding assay should be useful to determine the orientation of other membrane-interacting molecules.

Amino Acid Sequence↗

PubMed1998

Analysis of binding and membrane destabilization of phospholipid membranes by surfactant apoprotein B.

To further elucidate the nature of the molecular interactions of surfactant apoprotein B (SP-B) with phospholipid (PL) membranes, we studied the binding of SP-B to PL membranes and the lipid-dependency of its subsequent effects on leakage and fusion of membranes. SP-B binding to membranes was studied by labeling the protein with the fluorophore 7-nitro-2,1,3-benzoxadiazol-4-yl (NBD) and measuring the fluorescence of the labeled protein in the presence of varying amounts of dipalmitoylphosphatidylcholine-egg phosphatidylglycerol (DPPC-eggPG; 7-3). Leakage of contents from liposomes made of DPPC and varying molar fraction of egg phosphatidylcholine (eggPC) or eggPG was assessed by measuring the fluorescence of entrapped water-soluble probes ANTS and DPX. Fusion of membranes was assessed by measuring the fluorescence of membrane-bound NBD-phosphatidylethanolamine (NBD-PE) and rhodamine-PE (RHO-PE). We found that SP-B bound to PL membranes with high affinity and appeared to irreversibly cluster at the membrane surface, leading to graded release of the vesicle contents and eventually fusion of the membranes with increasing protein-lipid ratios. All lipid mixtures tested were susceptible to the membrane disruptive effects of SP-B, but DPPC-eggPG membranes displayed a biphasic response to increasing molar fractions of eggPG, whereas increasing fractions of eggPC elicited a monotonic response.

Animals↗

PubMed1997

Lipogastrins as potent inhibitors of viral fusion.

The rate and extent of membrane fusion is markedly sensitive to membrane interfacial properties. Lipopeptides with hydrophilic peptide moieties will insert into membranes, leaving the peptide portion at the membrane-water interface. In this work, we have used a lipopeptide composed of the peptide [Nle15]-gastrin-(2-17)-amide covalently linked to 1,2-diacyl-3-mercaptoglycerol-N(alpha)-maleoyl-beta-alanine to give DM-gastrin or DP-gastrin having 14 or 16 carbon atom acyl chains, respectively. The fluorescence emission from the two Trp residues of these lipopeptides exhibited little or no blue shift upon addition of liposomes of egg-phosphatidylethanolamine containing 5 mol% G(D1a). Iodide quenching of DP-gastrin fluorescence was also independent of lipid. These results indicate that the peptide moiety is exposed to the aqueous environment even though the lipopeptide is firmly anchored to the membrane. Both DM and DP-gastrin markedly raise the bilayer to hexagonal phase transition temperature of dipalmitoleoyl phosphatidylethanolamine. However, DM-E5 lowers this phase transition temperature. These lipopeptides have effects on the overall fusion of Sendai virus to liposomes in accord with their opposite effects on lipid curvature. The lipogastrins are potent inhibitors of viral fusion, while DM-E5 slightly promotes this process. Truncated forms of DM-gastrin are also inhibitory to viral fusion, but are less inhibitory than the full lipopeptide. Analysis of the fusion kinetics shows that DP-gastrin causes a reduction in the final extent of fusion and a marked lowering of the fusion rate constant. Binding of Sendai virus to the ganglioside receptor-containing liposomes was not affected. Consideration of the various contributions to the mechanism of inhibition of viral fusion suggests that effects of lipogastrin on membrane intrinsic monolayer curvature is of primary importance.

Amino Acid Sequence↗

PubMed1997

Emergence of template-and-sequence-directed (TSD) syntheses: II. A computer simulation model.

The initiation of the bio-geochemical scenario described in Part I serves in the present work as the basis for computer modeling, where the central process of the simulation algorithm. i.e., peptide-catalyzed oligomeric growth, is based on mass action equations. The computer model starts with a minimal system in which catalyzed growth processes of proto-RNA templates and small peptides take place, starting from their building blocks. The emerging populations of random oligomers also include a very small fraction of proto-tRNAs and a small fraction of catalytic peptides. Using simplifying assumptions regarding catalyzed proto-RNA template-replication, as well as selectivity of certain molecules and processes, the proportion of proto-tRNA in the proto-RNA molecular population increases rapidly; it is followed by TSD peptide synthesis, based on an ad hoc genetic code and specific peptide catalysts allocated for this synthesis. Consequently, a feedback system is initiated in which TSD peptides involved in the relevant catalytic reactions of the TSD syntheses also start to accumulate. The initial sporadic formation of TSD peptides is thus replaced gradually by cycles of positive feedback and autocatalysis characterized by accumulation of catalytic peptides and Proto-tRNAs and TSD-Reaction-Takeover. The model system which can be considered a 'toy model' can synthesize its templates and catalysts under a wide range of reaction parameters and initial concentrations, thus demonstrating a robustness which is essential for molecular evolution processes. The critical stage of the buildup of a molecular mechanism for the initiation of a minimal TSD reaction cycle has thus been described; because of the centrality of TSD reaction cycles in biology, it is assumed to be central also in the origin of life processes.

Adenosine Triphosphate↗

PubMed1997

Emergence of template-and-sequence-directed (TSD) syntheses: I. A bio-geochemical model.

A biogeochemical model for the evolution of template-and-sequence-directed (TSD) syntheses of biological templates (proto-RNAs) and catalysts (peptides) is described. A fluctuating environment characterized by hydrating (cool) and dehydrating (warm) phases with cycles of consecutive organic reactions, as well as a constant supply of the polymeric building blocks is assumed. The scenario starts with the catalyzed formation of a primordial population of small random peptides, based on the relatively-ineffective mineral catalysts. The resulting peptides initiate a catalytic takeover process, during which the catalytic functions are gradually taken over by peptides. The evolution of TSD peptides is based on a combination of Lahav's (1991) co-evolution and Moller and Janssen's (1990) specific recognition sites hypotheses. During the emergence of TSD systems the fraction of TSD peptides and proto-RNA constituents rises from almost insignificance to dominance in a TSD Reactions Takeover. The TSD system is characterized by autocatalysis, positive feedback loops and a primordial genetic code. The model is the basis for a computer program (Part II of present series).

Base Sequence↗

PubMed1996

Real-time kinetic measurements of the interactions between lactogenic hormones and prolactin-receptor extracellular domains from several species support the model of hormone-induced transient receptor dimerization.

Interactions of recombinant soluble prolactin receptors-extracellular domains (PRLR-ECDs) from rabbit, rat, and cow and human growth hormone receptor ECD with immobilized human growth hormone, several prolactins, and bovine placental lactogen were studied utilizing surface plasmon resonance. This method enables real-time kinetic measurements of the interactions and calculations of kinetic constants and of the stoichiometry of interaction, even in cases where only transient interactions occur. In contrast to gel filtration or crystallographic studies, where in most cases the interaction of PRLR-ECDs with various lactogenic hormones indicated formation of 1:1 complexes, our surface plasmon resonance experiments indicated in all cases the transient formation of a 2:1 complex. In most of the interactions the 2:1 complex was very unstable and underwent rapid dissociation to a 1:1 complex. This situation was particularly characteristic of homologous interactions involving hormone and receptor from the same species and was mainly attributed to increased dissociation constants. We suggest that as in the case of growth hormone PRLR activation occurs via hormone-induced transient homodimerization of the receptor, lasting only a few seconds, and that this may be sufficient to initiate the biological signal. Once the signal is initiated, the receptor dimer is no longer required. Its rapid dissociation to a 1:1 complex or to its components may even be advantageous in that it permits activation of additional receptors.

Animals↗

PubMed1996

Partial fusion activity of influenza virus toward liposomes and erythrocyte ghosts is distinct from viral inactivation.

Final extents of fusion of influenza virus (A/PR/8/34 strain) with neutral and partially acidic liposomes were monitored with (i) a fluorescence resonance energy-transfer assay in which the liposomes were labeled and (ii) by the dequenching of octadecylrhodamine, initially incorporated in the viral membrane. The latter assay was also employed in the fusion of influenza virus and Sendai virus with erythrocyte ghosts. In all cases, a phenomenon of partial fusion activity of the virus was observed, which is distinct from low pH inactivation. The unfused influenza or Sendai virions, which were separated by sucrose gradient centrifugation from liposomes or erythrocyte ghosts exhibited again partial fusion activity toward freshly added liposomes or ghosts, respectively. The conclusion is that the fraction of initially bound and unfused virions does not consist of defective particles, but rather of particles bound to the target membranes via inactive sites on the virus (or on cellular membranes), or else, partial fusion activity is a manifestation of a certain probability of production of fusion inactive sites by irreversible association of viral glycoproteins or peptides in the target membrane.

Energy Transfer↗

PubMed1996

Glycophorin as a receptor for Sendai virus.

Glycophorin A was reconstituted into large unilamellar vesicles of egg phosphatidylcholine by detergent dialysis. The observed overall rate of Sendai virus fusion increased approximately 4-fold between 0 and 0.006 mol % glycophorin, roughly proportional to the glycophorin content. However, no further increase in rate was observed at 0.02 mol % glycophorin. Treatment of reassembled glycophorin-liposomes with neuraminidase resulted in a significant decrease in the percent of viral fusion, confirming that the presence of sialic acid residues on glycophorin is essential for its role as a receptor. The sialic acid-containing glycolipid, the ganglioside GD1a, was also incorporated into phosphatidylcholine liposomes, either in addition to or in place of glycophorin A. Comparing, on the basis of sialic acid content, liposomes containing either glycophorin or GD1a, comparable rates and extents of fusion were found. However, on a molar basis glycophorin is much more effective. It was found that the addition of GD1a to glycophorin-containing liposomes only slightly increased the rate of fusion. This was largely due to an increase in the percent of virions capable of fusing.

Gangliosides↗

PubMed1996

Kinetics of phospholipid membrane fusion induced by surfactant apoproteins A and B.

Surfactant apoproteins A (SP-A) and B(SP-B) interact with the lipids of surfactant and such protein- lipid interactions may be of importance in several of the steps in the surfactant cycle. We analyzed the kinetics of fusion of dipalmitoylphosphatidylcholine-phosphatidyglycerol (DPPC:PG; 7:3, w/w) phospholipid vesicles induced by SP-B alone, in the presence of 5 mM calcium, and in the presence of calcium and SP-A. Membrane fusion was measured by the method of resonance energy transfer between non-exchangeable fluorophores incorporated in the membrane. Data were analyzed using a mass action kinetic model for membrane fusion between phospholipid vesicles. We found a SP-B dose-dependent increase in lipid mixing within a range of phospholipid concentration of 5 to 100 micromolar. Calcium caused a small additive increase in lipid mixing, but calcium and SP-A combined markedly increased lipid mixing induced by SP-B. Both aggregation and fusion rate constants increased with an increase in the SP-B/lipid ratio. In the presence of calcium and SP-A, the number of vesicles per fusion product markedly increased, as did the aggregation rate constants, whereas the fusion rate constants remained essentially unchanged.

Calcium↗

PubMed1996

Aggregation of phospholipid vesicles by water-soluble polymers.

Water-soluble polymers such as dextran and polyethylene glycol are known to induce aggregation and size growth of phospholipid vesicles. The present study addresses the dependence of these processes on vesicle size and concentration, polymer molecular weight, temperature, and compartmentalization of the vesicles and polymers, using static and dynamic light scattering. Increasing the molecular weight of the polymers resulted in a reduction of the concentration of polymer needed for induction of aggregation of small unilamellar vesicles. The aggregation was fully reversible (by dilution), within a few seconds, up to a polymer concentration of at least 20 wt %. At relatively low phosphatidylcholine (PC) concentrations (up to approximately 1 mM), increasing the PC concentration resulted in faster kinetics of aggregation and reduced the threshold concentration of polymer required for rapid aggregation (CA). At higher PC concentrations, CA was only slightly dependent on the concentration of PC and was approximately equal to the overlapping concentration of the polymer (C*). The extent of aggregation was similar at 37 and 4 degrees C. Aggregation of large unilamellar vesicles required a lower polymer concentration, probably because aggregation occurs in a secondary minimum (without surface contact). In contrast to experiments in which the polymers were added directly to the vesicles, dialysis of the vesicles against polymer-containing solutions did not induce aggregation. Based on this result, it appears that exclusion of polymer from the hydration sphere of vesicles and the consequent depletion of polymer molecules from clusters of aggregated vesicles play the central role in the induction of reversible vesicle aggregation. The results of all the other experiments are consistent with this conclusion.

Dextrans↗

PubMed1996

Effect of cholesterol and charge on pore formation in bilayer vesicles by a pH-sensitive peptide.

The effect of cholesterol on the bilayer partitioning of the peptide GALA (WEAALAEALAEALAEHLAEALAEALEALAA) and its assembly into a pore in large unilamellar vesicles composed of neutral and negatively charged phospholipids has been determined. GALA undergoes a conformational change from a random coil to an amphipathic alpha-helix when the pH is reduced from 7.0 to 5.0, inducing at low pH leakage of contents from vesicles. Leakage from neutral or negatively charged vesicles at pH 5.0 was similar and could be adequately explained by the mathematical model (Parente, R. A., S. Nir, and F. C. Szoka, Jr., 1990. Mechanism of leakage of phospholipid vesicle contents induced by the peptide GALA. Biochemistry. 29:8720-8728) which assumed that GALA becomes incorporated into the vesicle bilayer and irreversibly aggregates to form a pore consisting of 10 +/- 2 peptides. Increasing cholesterol content in the membranes resulted in a reduced efficiency of the peptide to induce leakage. Part of the cholesterol effect was due to reduced binding of the peptide to cholesterol-containing membranes. An additional effect of cholesterol was to increase reversibility of surface aggregation of the peptide in the membrane. Results could be explained and predicted with a model that retains the same pore size, i.e., 10 +/- 2 peptides, but includes reversible aggregation of the monomers to form the pore. Resonance energy transfer experiments using fluorescently labeled peptides confirmed that the degree of reversibility of surface aggregation of GALA was significantly larger in cholesterol-containing liposomes, thus reducing the efficiency of pore formation.

Amino Acid Sequence↗

PubMed1996

Reversible surface aggregation in pore formation by pardaxin.

The mechanism of leakage induced by surface active peptides is not yet fully understood. To gain insight into the molecular events underlying this process, the leakage induced by the peptide pardaxin from phosphatidylcholine/ phosphatidylserine/cholesterol large unilamellar vesicles was studied by monitoring the rate and extent of dye release and by theoretical modeling. The leakage occurred by an all-or-none mechanism: vesicles either leaked or retained all of their contents. We further developed a mathematical model that includes the assumption that certain peptides become incorporated into the vesicle bilayer and aggregate to form a pore. The current experimental results can be explained by the model only if the surface aggregation of the peptide is reversible. Considering this reversibility, the model can explain the final extents of calcein leakage for lipid/peptide ratios of > 2000:1 to 25:1 by assuming that only a fraction of the bound peptide forms pores consisting of M = 6 +/- 3 peptides. Interestingly, less leakage occurred at 43 degrees C, than at 30 degrees C, although peptide partitioning into the bilayer was enhanced upon elevation of the temperature. We deduced that the increased leakage at 30 degrees C was due to an increase in the extent of reversible surface aggregation at the lower temperature. Experiments employing fluorescein-labeled pardaxin demonstrated reversible aggregation of the peptide in suspension and within the membrane, and exchange of the peptide between liposomes. In summary, our experimental and theoretical results support reversible surface aggregation as the mechanism of pore formation by pardaxin.

Amino Acid Sequence↗

PubMed1995

Target cell membrane sialic acid modulates both binding and fusion activity of influenza virus.

Influenza virus binds to cell surface sialic acid receptors, and following endocytosis fuses with the endosome membrane at low pH. Whether sialic acid plays a role in the virus-cell membrane fusion step is not known. We investigated the effect of the removal of cell membrane sialic acid on the fusion activity of influenza virus (A/PR/8/34 strain) toward human T lymphocytic leukemia (CEM) cells at low pH. Fusion was monitored by fluorescence dequenching of octadecylrhodamine incorporated in the virus membrane. Removal of sialic acid by neuraminidase resulted in a drastic reduction in both viral binding and fusion. The association of the virus with neuraminidase-treated cells was enhanced at pH 5, compared to that at neutral pH, probably due to the unfolding of the hemagglutinin and the resulting increase in viral surface hydrophobicity, but the fusion capacity of the virus was reduced significantly. The results were analysed with a mass-action kinetic model which could explain and predict the kinetics of fusion. Our results indicate that binding of influenza virus to sialic acid residues on the cell surface leads to rapid and extensive fusion and partially inhibits the low pH-induced viral inactivation.

Cell Line↗

PubMed1995

Potent inhibition of viral fusion by the lipophosphoglycan of Leishmania donovani.

Lipophosphoglycan (LPG) is an amphiphile produced by Leishmania. Its chemical structure consists of a hydrophilic flexible polymer of repeating PO4-6Gal beta 1-4Man alpha 1 units (on average 16 units) linked via a hexasaccharide core to a lyso-1-O-alkyl-P1 membrane anchor. In the study of viral fusion we report in this paper, we have introduced LPG into human erythrocyte ghost (HEG) membranes, with the purpose of understanding how the LPG-induced surface-structural changes may modulate the interactions between a viral envelope and the HEG membranes. We have found that LPG, when incorporated at very low concentrations into intact human erythrocyte membranes, strongly inhibits Sendai virus-induced hemolysis. When incorporated into HEGs, it reduces the binding of both Sendai and influenza viruses to HEGs; furthermore, it strongly inhibits the overall viral fusion to HEGs, being among the most potent known inhibitors. We have also shown that LPG stabilizes the bilayer structure of phosphatidylethanolamine against the formation of an inverted-hexagonal structure. We suggest that LPG may give rise to an effective "steric repulsion" between the viral and HEG membranes, thereby modulating some specific modes of interaction between viral-target membranes in the overall fusion process; LPG may also modulate the bending rigidity and the spontaneous curvature of the HEG membrane in the direction of making the destabilization and rearrangement of the underlying lipid bilayer more difficult.

Animals↗

PubMed1995

The role of the ganglioside GD1a as a receptor for Sendai virus.

The ganglioside GD1a, which serves as a receptor for Sendai virus, also affects lipid polymorphism as determined by 31P nuclear magnetic resonance. The ganglioside promotes the formation of isotropic structures in monomethyldioleoylphosphatidylethanolamine. GD1a also raises the bilayer to hexagonal phase transition temperature of this lipid. The effects of GD1a on the kinetics of viral fusion can be understood on the basis of its role in facilitating the binding of Sendai virus to target membranes as well as its effects on membrane physical properties. Fusion of Sendai virus with liposomes composed of egg phosphatidylethanolamine is particularly sensitive to the presence of ganglioside. In the absence of ganglioside no fusion is observed due to the absence of virus binding to the target membrane. Between 2 and 6 mol % GD1a in egg phosphatidylethanolamine liposomes there is a marked increase in the rate constant of binding of the virus to the liposome but a decrease in the fusion rate constant. The latter effect is found to be common to a number of other amphiphiles that raise the bilayer to hexagonal phase transition temperature. The ganglioside enhances virus binding to liposomes of all the compositions studied, but leakage rates and fusion rate constants are either unaffected or reduced. In the systems studied, the enhanced formation of isotropic structures in liposomes containing the ganglioside does not enhance the kinetics of the actual fusion reaction.

Gangliosides↗

PubMed1994

Capacities of pardaxin analogues to induce fusion and leakage of negatively charged phospholipid vesicles are not necessarily correlated.

Peptide-induced vesicle fusion is frequently accompanied by leakage of vesicle contents. To determine the correlation between these two processes, we studied the interaction of the amphiphilic peptide pardaxin and two of its analogues with large unilamellar vesicles composed of phosphatidylserine. A pardaxin analogue with a positive charge at both its C- and N-termini induced significantly more fusion but less leakage than the parent peptide. Fusion and leakage were studied with large unilamellar vesicles of two sizes. Aggregation of vesicles was found to be the rate-limiting step in the overall fusion process induced by the peptides. The rates and extents of fusion, determined by membrane mixing, increase in vesicle size, and mixing of aqueous contents, were significantly enhanced in the presence of 2.5-5 mM Mg2+ which promoted vesicle aggregation. Model calculations showed that increasing the peptide to lipid ratio resulted in a parallel increase in the fusion rate constants. As the average vesicle diameter was increased, the extent of leakage was enhanced, as more peptide molecules were bound to each vesicle. The mode of leakage induced by the peptides was also investigated. Our results suggest that the potency of a peptide to induce vesicle fusion is not necessarily associated with its capacity to induce leakage, and we further elucidate how these capacities depend on the structures of the peptides.

Amino Acid Sequence↗