3-Amidoquinuclidine derivatives: synthesis of compounds and inhibition of butyrylcholinesterase

The synthesis of racemic and enantiomerically pure 3-butanamidoquinuclidines ((+/-)-Bu, (R)-Bu and (S)-Bu), (1-3) and 3-benzamidoquinuclidines ((+/-)-Bz, (R)-Bz, and (S)-Bz), (4-6) is described. The N-quaternary derivatives, N-benzyl-3-butanamidoquinuclidinium bromides ((+/-)-BnlBu, (R)-BnlBu and (S)-BnlBu), (7-9) and N-benzyl-3-benzamidoquinuclidinium bromides ((+/-)-BnlBz, (R)-BnlBz and (S)-BnlBz), (10-12) were subsequently synthesized. The interaction of the four enantiomerically pure quaternary derivatives with horse serum butyrylcholinesterase (BChE) was tested. All tested compounds inhibited the enzyme. The best inhibitior of the enzyme was (S)-BnlBz with a K(i) = 3.7 microM. The inhibitor potency decreases in order (S)-BnlBz > (R)-BnlBz > (R)-BnlBu > (S)-BnlBu.     

Electrochemical characterization and application of azurin-modified gold electrodes for detection of superoxide

A novel biosensor for superoxide radical (O(2)(*-)) detection based on Pseudomonas aeruginosa azurin immobilized on gold electrode was designed. The rate constant of azurin reduction by O(2)(*-) was found to be 10(5)M(-1)s(-1) in solution and five times lower, i.e., 0.2 x 10(5)M(-1)s(-1), for azurin coupled to gold by 3,3'-dithiobis(sulfosuccinimidylpropionate) (DTSSP). The electron transfer rate between the protein and the electrode ranged from 2 to 6s(-1). The sensitivity of this biosensor to O(2)(*-) was 6.8 x 10(2)Am(-2)M(-1). The response to the interference substances, such as uric acid, H(2)O(2), and dimethylsulfoxide was negligible below 10 microM. The electrode was applied in three O(2)(*-) generating systems: (i) xanthine oxidase (XOD), (ii) potassium superoxide (KO(2)), and (iii) stimulated neutrophil granulocytes. The latter was compared with luminol-amplified chemiluminescence. The biosensor responded to O(2)(*-) in all three environments, and the signals were antagonized by superoxide dismutase.     

Thermodynamics of hydrolysis of oligosaccharides

Microcalorimetry has been used to determine enthalpy changes for the hydrolysis of a series of oligosaccharides. High-pressure liquid chromatography was used to determine the extents of reaction and to check for any possible side reactions. The enzyme glucan 1,4-alpha-glucosidase was used to bring about the following hydrolysis reactions: (A) maltose(aq) + H2O(liq) = 2D-glucose(aq); (B) maltotriose(aq) + 2H2O(liq) = 3D-glucose(aq); (C) maltotetraose(aq) + 3H2O(liq) = 4D-glucose(aq); (D) maltopentaose(aq) + 4H2O(liq) = 5D-glucose(aq); (E) maltohexaose(aq) + 5H2O(liq) = 6D-glucose(aq); (F) maltoheptaose(aq) + 6H2O(liq) = 7D-glucose(aq); (G) amylose(aq) + nH2O(liq) = (n + 1) D-glucose(aq); and (H) panose(aq) + 2H2O(liq) = 3D-glucose(aq); (J) isomaltotriose(aq) + 2H2O(liq) = 3D-glucose(aq). The enzyme beta-fructofuranosidase was used for the reactions: (K) raffinose(aq) + H2O(liq) = alpha-D-melibiose(aq) + D-fructose(aq); and (L) stachyose(aq) + H2O(liq) = o-alpha-D-galactopyranosyl-(1----6)- alpha-o-D-galactopyranosyl-(1----6)-alpha-D-glucopyranose + D-fructose(aq). The results of the calorimetric measurements (298.15 K, 0.1 M sodium acetate buffer, pH 4.44-6.00) are: delta H0A = -4.55 +/- 0.10, delta H0B = -9.03 +/- 0.10, delta H0C = -13.79 +/- 0.15, delta H0D = -18.12 +/- 0.10, delta H0E = -22.40 +/- 0.15, delta H0F = -26.81 +/- 0.20, delta H0H = 1.46 +/- 0.40, delta H0J = 11.4 +/- 2.0, delta H0K = -15.25 +/- 0.20, and delta H0L = -14.93 +/- 0.20 kJ mol-1. The enthalpies of hydrolysis of two different samples of amylose were 1062 +/- 20 and 2719 +/- 100 kJ mol-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of the effectiveness of the interaction of ribo- and deoxyriboprimers with DNA-polymerase from the human placenta

The Km and Vmax values for primers d(pA)n, d(pT)n, r(pA)n, r(pU)n where n = 1-16, were compared. The Km values for minimal primers dTMP, dAMP, rUMP, rAMP were found to be 48, 71, 602 and 602 microM, respectively. The Vmax value for any NMP made up approximately 7% of that for (pN)10. The lengthening of any primer per one mononucleotide unit for n from 1 to 10 resulted in the decrease of the Km value 1.8-fold and the increase of the Vmax value 1.35-fold. The ratios of the Km values for primers r(pA)n-d(pA)n and r(pU)n-d(pT)n were 7.5 and 12.5, respectively, for any n. The Km value for [d[pT)8]r(pU) primer was the same as for r(pU)9, but not for d(pT)9. Decanucleotide [d(Tp)9]ddT interacted with the polymerase competitively to the template, but not to the primer. The primer's 3'-OH group was supposed to form the hydrogen bond with the enzyme. The absence of 3'-hydroxygroup in [d(Tp)9]ddT resulted in its inability to compete effectively with the primer. The difference of the affinity of ribo- and deoxyriboprimers is due, apparently, to the existence of the different conformation of the furanose rings in the ribose and deoxyribose.     

Alteration of rheological properties of human erythrocytes by crosslinking of membrane proteins

The crosslinking of membrane proteins of human erythrocytes by diamide (diazene dicarboxylic acid bis(N,N-dimethylamide) ) was quantified by 4% polyacrylamide gel electrophoresis in 1% sodium dodecyl sulfate. The relation between the crosslinking of membrane proteins and erythrocyte functions (rheological and oxygen transporting) was quantitatively examined. (i) The crosslinking of membrane protein was induced by diamide, without changing the shape and the contents of intracellular organic phosphates (adenylates and 2,3-diphosphoglycerate). The intensity of spectrin 2 in SDS-polyacrylamide gel electrophoresis decreased proportionally to diamide concentration. The percentage decrease in spectrin 2 (using band 3 as an internal standard) was the most appropriate indicator for crosslinking ("% crosslinking'). (ii) The suspension viscosity of erythrocytes increased in proportion to the percentage of crosslinking, in the range of applied shear rates of 3.76-752 s-1. (iii) Erythrocyte deformability (measured by a high-shear rheoscope) was reduced by the crosslinking. The change was detectable even at 5% crosslinking. (iv) Rouleaux formation (measured by a television image analyzer combined with a low-shear rheoscope) was inhibited by the crosslinking. The inhibition was also sensitively detected at more than 5% crosslinking. (v) Hemoglobin in erythrocytes was chemically modified by higher dose of diamide (probably by the binding of diamide with sulfhydryl groups). Also the oxygen affinity of hemoglobin increased and the heme-heme interaction decreased. (vi) The reduction of the crosslinking of membrane proteins by dithiothreitol apparently reversed the intensity of spectrin bands in SDS-polyacrylamide gel electrophoresis and the erythrocyte functions (the suspension viscosity and the deformability), though not completely.     

Investigations of the possible pharmacological effects of organotin(II) complexes

Antitumour, antifertility and histopathological investigations were carried out on male rats by the use of organotin complexes. The organotin complexes were synthesized by the alkylation of [Sn(TAML(n))Cl(2)] (n=1-4 and TAML(n) represents the tetraazamacrocyclic ligands) in the presence of CH(3)I or C(2)H(5)Br. The structures of all the complexes have been established on the basis of elemental analyses, conductivity measurements, IR, (1)H NMR, (13)C NMR, (119)Sn NMR and X-ray spectral data. The antitumour effect of the compounds was examined on swiss mice. The results obtained clearly indicated that the compounds, [C(2)H(5)Sn(TAML(3))C(5)H(5)N] and [C(2)H(5)Sn(TAML(4))C(5)H(5)N] display effective antitumour activity. The emphasis has been given on in vivo study on male albino rats (Rattus norvegicus) by performing serum analyses, blood analyses and fertility test.     

Mechanism of chaperone-like activity. Suppression of thermal aggregation of betaL-crystallin by alpha-crystallin

Thermal denaturation and aggregation of beta(L)-crystallin from bovine lens have been studied using differential scanning calorimetry (DSC) and dynamic light scattering (DLS). According to the DLS data, the distribution of the beta(L)-crystallin aggregates by their hydrodynamic radius (R(h)) remains monomodal to the point of precipitating aggregates (sodium phosphate, pH 6.8; 100 mM NaCl; 60 degrees C). The size of the start aggregates (R(h,0)) and duration of the latent stage (t(0)) leading to the formation of the start aggregates have been determined from the light scattering intensity versus the hydrodynamic radius plots and the dependences of R(h) on time. The R(h,0) value remains constant at variation of the beta(L)-crystallin concentration, whereas the t(0) value increases with diminishing beta(L)-crystallin concentration. The suppression of beta(L)-crystallin aggregation by alpha-crystallin is connected with the decrease in the R(h,0) value and increase in the t(0) value. In the presence of alpha-crystallin the aggregate population is split into two components. The first component is represented by stable aggregates whose size remains constant in time. The aggregates of the other kind grow until they reach the size characteristic of aggregates prone to precipitation. The DSC data show that alpha-crystallin has no appreciable influence on thermal denaturation of beta(L)-crystallin.     

Dependence of 3'-5-exonuclease activity of a fragment of Klenow DNA polymerase I from Escherichia coli on the length and structure of the cleaved oligonucleotide

The Km and vmax values for oligothymidylates d(pT)2-16 in reaction of 3'-5'-exonuclease hydrolysis catalyzed by Klenow fragment were measured in the absence and presence of poly(dA) template without the poly(dA), the Km values for oligonucleotides are slightly dependent on their length. The rate of oligothymidylates hydrolysis increases with their length and for d(pT)16 it is about 190-times higher than for d(pT)2. The addition on poly(dA) does not lead to an essential change of the Km values for d(pT)2-16, but raises the rate of d(pT)2-7 hydrolysis 2-17-fold and at the same time lowers the efficiency of d(pT)8-16 hydrolysis. The Km values for d(pC)10, d(pA)19 and d(pT)10 are nearly the same. However the velocity of d(pC)10 hydrolysis is approximately 1,2 and 7,8-times higher than for d(pA)10 and d(pC)10, respectively d(pC)10, d(pA)10 and d(pT)10 under conditions of interaction with the template-binding site raise the rate of hydrolysis of d(pT)2 combined with the exonuclease center, with various efficiency. Under similar conditions, d(pT)8, d(pT)10 and d(pT)16 as templates activated hydrolysis of d(pT)2. The dependence of the Klenow fragment exonuclease activity both on the length and structure of the template and on the length of the hydrolyzed oligonucleotide was suggested.     

Identification of functionally important residues of Arabidopsis thaliana S-adenosylmethionine decarboxylase

The Arabidopsis thaliana S-adenosylmethionine decarboxylase (AdoMetDC) cDNA (GenBank(TM) U63633) was cloned, and the AdoMetDC protein was expressed, purified, and characterized. The K(m) value for S-adenosylmethionine (AdoMet) is 23.1 microM and the K(i) value for methylglyoxal bis-(guanylhydrazone) (MGBG) is 0.15 microM. Site-specific mutagenesis was performed on the AdoMetDC to introduce mutations at conserved cysteine (Cys(50), Cys(83), and Cys(230)) and lysine(81) residues, chosen by examination of the conserved sequence and proved to be involved in enzymatic activity by chemical modification. The AdoMetDC mutants K81A and C83A retained up to 60 and 10% of wild type activity, respectively, demonstrating that lysyl and sulfhydryl groups are required for full catalytic activity. However, changing Cys(50) and Cys(230) to alanine had minimal effects on the catalytic activity. Changing Lys(81) to alanine produced an altered substrate specificity. When lysine was used as a substrate instead of AdoMet, the substrate specificity for lysine increased 6-fold. The K(m) value for AdoMet is 11-fold higher than that of the wild type, but the V(max) value is more than 60%. Taken together, the results suggest that the lysine(81) residue is critical for substrate binding.     

The Genetic Structure of Natural Populations of DROSOPHILA MELANOGASTER. Xvi. Excess of Additive Genetic Variance of Viability

About 500 second and 500 third chromosomes were extracted, using the marked inversion technique, from the Orlando-Lake Placid, Florida, population. From the experiments using these chromosomes, the following findings were obtained: (1) The frequencies of lethal-carrying chromosomes were 0.37 in the second and 0.55 in the third chromosomes. (2) The size of the population was estimated to be effectively infinite, on the basis of the allelism rate of lethal-carrying chromosomes. (3) The detrimental and lethal loads for viability were, respectively, 0.40 and 0.45 for the second and 0.52 and 0.78 for the third chromosomes. Consequently, the detrimental to lethal load ratio is 0.90 for the second and 0.67 for the third chromosomes. (4) Lethal genes were shown to be deleterious when heterozygous. (5) The average degree of dominance for mildly deleterious genes (viability polygenes) was estimated to be nearly 0.5, although the confidence interval is large. (6) Additive (sigma( 2) (A)) and dominance (sigma(2) ( D)) variances of viability were estimated by using a partial diallel cross method. The results were (see PDF) and (see PDF) for the second chromosomes. (7) Environmental variances of viability were estimated. The result indicates that the heterozygotes are more homeostatic than the homozygotes. The most striking finding is that the additive variance is larger than expected on the classical hypothesis from the detrimental load. Several possible explanations for the discrepancy are offered. The most likely cause, we suggest, is genotype-environment interaction (diversifying selection) acting on viability polygenes. Overdominance is inconsistent with the low dominance variance, and frequency-dependent selection also appears unlikely as an explanation.     

Effect of kyotorphin on the reactivity of hippocampal neurons

The effects of kyotorphin (Tyr-Arg) on CA1 and CA3 field responses were studied on rat hippocampal slice preparations. Slice perfusion with 10(-6)-10(-4) M of kyotorphin resulted in reactivity changes both in mossy fibers (CA3) and Schaffer collaterals (CA1). The principal effect was the increase in pop-spike amplitude. Kyotrophin (10(-6)-10(-5) M) and metenkephalin (10(-7)-10(-6) M) were found to produce similar reactivity changes (facilitation) in CA1 region of most preparations. However, kyotorphin effect, in contrast to enkephalin-induced facilitation was not blocked by naloxone. The data suggest that the mechanisms of kyotorphin action in the hippocamp are not related to endogenous enkephalin release.     

Spectroscopic and electrochemical properties of the Met86Gln mutant of Achromobacter cycloclastes pseudoazurin

The mutant replacing the Met86 ligand of Achromobacter cycloclastes pseudoazurin (Ac-pAz) with Gln has been prepared and spectroscopically and electrochemically characterized. Ac-pAz has four ligands (2His, Cys, and Met) and donates one electron to its cognate Cu-containing nitrite reductase (Ac-NIR). The mutant ([Met86Gln]pAz) shows the electronic absorption and CD spectra considerably similar to those of zucchini mavicyanin (Mv) and lacquer and cucumber stellacyanins (St) having 2His, Cys, and Gln. The EPR signal of the mutant has an axial character, although those of Mv and St show rhombic signals. The findings indicate that the Cu site having Gln might be a distorted trigonal geometry. The half-wave potentials (E(1/2)) of [Met86Gln]pAz and the intermolecular electron-transfer rate constant (kET) from the mutant to Ac-NIR were determined by cyclic voltammetry at pH 7.0 and 25 degrees C. The E(1/2) is +134 mV (versus NHE) and the coordination of Gln instead of Met negatively shifts the E(1/2) of Ac-pAz (+260 mV (versus NHE)). The kET of [Met86Gln]pAz (1.2x10(6) M(-1) s(-1)) is larger than that of the recombinant Ac-pAz (7.5x10(5) M(-1) s(-1)).     

Characterization of sialidase from bloodstream forms of Trypanosoma vivax

Sialidase (EC: 3.2.1.18) from Trypanosoma vivax (Agari Strain) was isolated from bloodstream forms of the parasite and purified to apparent electrophoretic homogeneity. The enzyme was purified 77-fold with a yield of 32% and co-eluted as a 66-kDa protein from a Sephadex G 110 column. The T. vivax sialidase was optimally active at 37 degrees C with an activation energy (E(a)) of 26.2 kJ mole(-1). The pH activity profile was broad with optimal activity at 6.5. The enzyme was activated by dithiothreitol and strongly inhibited by para-hydroxy mercuricbenzoate thus implicating a sulfhydryl group as a possible active site residue of the enzyme. Theenzyme hydrolysed Neu5Ac2,3lac and fetuin. It was inactive towards Neu5Ac2,6lac, colomic acid and the gangliosides GM1, and GDI. Initial velocity studies, for the determination of kinetic constants with fetuin as substrate gave a V(max) of 142.86 micromol h(-1) mg(-1) and a K(M) of 0.45 mM. The K(M) and V(max) with Neu5Ac-2,3lac were 0.17 mM and 840 micromole h(-1) mg(-1) respectively. The T. vivax sialidase was inhibited competitively by both 2,3 dideoxy neuraminic acid (Neu5Ac2,3en) and para-hydroxy oxamic acid. When ghost RBCs were used as substrates, the enzyme desialylated the RBCs from camel, goat, and zebu bull. The RBCs from dog, mouse and ndama bull were resistant to hydrolysis.     

Spectroscopy, cytotoxicity and DNA-binding of the lanthanum(III) complex of an L-valine derivative of 1,10-phenanthroline

The interaction of the lanthanum(III) La(III)-L (L=N,N'-bis-(1-carboxy-2-methylpropyl)-1,10-phenanthroline-2,9-dimethanamine) complex with calf thymus DNA was studied by electronic spectra, fluorescence spectra and circular dichroic spectra. The La(III)-L complex was assayed for antitumor activity in vitro against the HL-60 (the human leucocytoma) cells, HCT-8 (the human coloadenocarcinoma) cells, BGC-823 (the human carcinoma of stomach) cells, Bel-7402 (the human liver carcinoma) cells and KB (the human nasopharyngeal carcinoma) cells. The results show that the La(III)-L complex has activity against HL-60 cells, Bel-7402 cells and KB cells. Moreover, it is slightly more effective against Bel-7402 cell line than cisplatin. Using ethidium bromide as a fluorescence probe, the binding mode of the La(III)-L complex to calf-thymus DNA was studied spectroscopically. For comparison, the same measurements were carried out with La(III)-Phen [La(III)-1,10-phenanthroline complex] and La(III)-Val [La(III)-L-valine complex]. The results indicate that the La(III)-L and La(III)-Phen complexes possibly interact with calf-thymus DNA by both intercalative and coordination binding, whereas the La(III)-Val complex interacts with calf-thymus DNA by coordination binding. Kinetics of binding of the three complexes to DNA is for the first time studied using ethidium bromide as a fluorescence probe with stopped-flow spectrophotometer under pseudo-first-order condition. The strong two-step mechanisms in the process of the La(III)-L and La(III)-Phen complexes and one step in the process of the complex La(III)-Val interacting with DNA are observed, and the k(obs) (observed pseudo-first-order rate constant) and E(a) (observed energy of activation) values of binding to DNA are obtained.     

Dephosphorylation of phosphoproteins and synthetic phosphopeptides. Study of the specificity of the polycation-stimulated and MgATP-dependent phosphorylase phosphatases

The substrate specificity of different forms of polycation-stimulated (PCSH, PCSL, and PCSC) phosphorylase phosphatases and of the catalytic subunit of the MgATP-dependent protein phosphatase from rabbit skeletal muscle was investigated. This was done, with phosphorylase a as the reference substrate, using the synthetic phosphopeptides patterned after the phosphorylated sites of pyruvate kinase (type L) (Arg2-Ala-Ser(32P)-Val-Ala (S2), and its Thr(32P) substitute (T4)), inhibitor-1 (Arg4-Pro-Thr(32P)-Pro-Ala (T5), Arg2-Pro-Thr(32P)-Pro-Ala (T1), and its Ser(32P) substitute (S1)), and some modified phosphopeptides (Arg2-Ala-Thr(32P)-Pro-Ala (T2) and Arg2-Pro-Thr(32P)-Val-Ala (T3)), all phosphorylated by cyclic AMP-dependent protein kinase. In addition, casein(Thr-32P), phosphorylated by casein kinase-2, was also tested. The PCS phosphatases show a striking preference for the T4 configuration, PCSC being the least efficient. The catalytic subunit of the MgATP-dependent phosphatase was almost completely inactive toward all these substrates. As shown for the PCSH phosphatase, and comparing with T4, the two proline residues flanking the Thr(P) in T1 and T5, just as in inhibitor-1, drastically imparied the dephosphorylation by lowering the Vmax and not by affecting the apparent Km. The C-terminal proline (as in T2) by itself represents a highly unfavorable factor in the dephosphorylation. The critical effect of the sequence X-Thr(P)-Pro or Pro-Thr(P)-Pro (T1, T2, T5, and inhibitor-1) can be overcome by manganese ions. The additional finding that this is not the case with the Pro-Ser(P)-Pro sequence (S1) suggests that the effect of Mn2+ is highly substrate specific. These observations show the considerable importance of the primary structure of the substrate in determining the specificity of the protein phosphatases.     

The effects of starvation, environmental temperature and injury on the rate of disposal of glucose by the rat

1. The disposal rate of glucose, R, given by R=k(v)Q, where Q is the quantity of plasma glucose and k(v) is a rate coefficient, was determined from the disappearance of [U-(14)C]-glucose from blood after single intravenous injection. Values of R should be close to the carbohydrate oxidation rate in the states investigated. 2. Normal rats (i) experimental methodology was studied. The best (single sampling) method gave the following results. (ii) The plasma glucose concentration (C(p)) and R were temporarily increased by the stress of handling and injection. (iii) R was increased by decreasing the environmental temperature from 29 degrees C to 20 degrees C in line with previously published (Stoner & Marshall, 1971) changes in total body O(2) consumption. (iv) Starvation decreased R such that R=constantxC(p) (2). (v) The results suggested some central control of cell permeability to glucose. 3. Injured post-absorptive rats were studied in the ebb phase after three severe injuries: scalding at 20 degrees and 29 degrees C (non-lethal) and bilateral hind-limb ischaemia at 20 degrees C (85% mortality). (i) Handling and injection did not affect C(p). (ii) The rise in C(p) after injury was not closely correlated with its severity. (iii) The value of R was nearly independent of severity. (iv) Unlike in normal rats R varied little with ambient temperature (in line with O(2) consumption) or with C(p). Values of k(v) varied inversely as C(p). (v) The results were explained in terms of a centrally integrated response to injury involving the hypothalamus which over-rode the controls operating in normal rats. Hormonal factors are discussed.     

Evidence for a crucial role of neutrophil-derived serine proteases in the inactivation of interleukin-6 at sites of inflammation

The bioactivity of interleukin-6 (IL-6) was found to be dramatically reduced in fluids from sites of inflammation. Here, we provide evidence that the neutrophil-derived serine proteases elastase, proteinase 3 and cathepsin G are mainly involved in its degradation and subsequent inactivation. The initially hydrolyzed peptide bonds were detected to be Val(11)-Ala(12) and Leu(19)-Thr(20) (elastase), Phe(78)-Asn(79) (cathepsin G) and Ala(145)-Ser(146) (proteinase 3). The soluble IL-6 receptor elicits a protective effect against the IL-6 inactivation by cathepsin G only. The inactivation of IL-6 by neutrophil-derived serine proteases might act as a feedback mechanism terminating the IL-6-induced activation of neutrophils.     

Studies of the receptor-bound conformation of alphaIIbbeta3 antagonists by 15N-edited NMR spectroscopy

We report the results of NMR studies and computer simulations of potent antagonists reflective of the alpha(IIb)beta(3) receptor-bound conformations. The peptides c[Mpa-(15)N-Arg(1)-(15)N-Gly(2)-(15)N-Asp(3)-(15)N-Phe(4)-(15)N-Arg(5)-Cys]-NH(2) (Phe-Arg analog) (Mpa: 3-mercaptopropionic acid) and c[Mpa-(15)N-Arg(1)-(15)N-Gly(2)-(15)N-Asp(3)-(15)N-Asp(4)-(15)N-Val(5)-Cys]-NH(2) (Asp-Val analog) were subjected to (15)N-edited NMR experiments to study the conformations of these peptides in the absence and in the presence of alpha(IIb)beta(3) receptor. The NMR studies of the Phe-Arg analog, a selective alpha(IIb)beta(3) antagonist, resulted in distinctly different experimental data in the presence and absence of the receptor. The computer simulations for this peptide resulted in one large family of structures consistent with the experimental data. This conformation suggests a type I beta-turn spanning residues Arg(1) and Gly(2) when bound to the receptor and we were able to establish a model for the three dimensional arrangement of the pharmacophores. The studies on the Asp-Val analog, an alpha(v)beta(3) antagonist that binds to the alpha(IIb)beta(3) with moderate affinity, resulted in conformations that are not as well defined as those for the Phe-Arg analog but are consistent with the model established for this analog. These results are important for the design of novel alpha(IIb)beta(3) antagonists.