Tripeptide Molecule Research Articles

КОНФОРМАЦИОННЫЕ СВОЙСТВА И ЭЛЕКТРОННАЯ СТРУКТУРА ПРОТИВООПУХОЛЕВОГО АГЕНТА TYR-SER-LEU

Molecular modeling methods were used to study the features of the spatial and electronic structure of the antitumor tripeptide YSL (Tyr-Ser-Leu), developed by Chinese scientists. The conformational analysis of the molecule revealed a limited set of its energetically preferable conformational states in a certain range of relative energy. The nature of the forces stabilizing the low-energy conformations of the tripeptide molecule was determined. As a result of the study, the energetically preferable ranges of dihedral angles, the energy contributions of interresidual interactions and hydrogen bonds, as well as the mutual arrangement of residues and their side chains in low-energy conformations of the tripeptide were also determined. Using the methods of molecular mechanics, the energy contributions of intramolecular interactions in low-energy conformational states of the molecule were obtained. Based on quantum-chemical calculations, the distribution of electron density and the values of dipole moments of the most optimal spatial structures of the YSL tripeptide molecule were determined. The reactivity of the tripeptide was also studied by quantum chemical calculations based on the obtained electronic characteristics of each low-energy conformation of the molecule. Using the calculated coordinates of the atoms of the energetically preferable structures of the molecule, their molecular models were built, the comparison of which makes it possible to identify the structural criteria necessary to create a drug suitable for clinical use.

Green synthesis of carbon dots from fish scales for selective turn off-on detection of glutathione.

Carbon dots as fluorescent probes were fabricated using readily available grass carp fish scales as the carbon source via one-step synthesis based on a pyrolytic reaction. The as-prepared grass carp fish scale carbon dots (GF-CDs) exhibited good biocompatibility and excellent optical properties with a high fluorescence quantum yield of 23.8%. Glutathione (GSH) is an essential small tri-peptide molecule present in every body cell and plays a crucial role in vivo and performs a wide range of biological functions. Ag+ can effectively quench the fluorescence of GF-CDs because of the electron transfer between GF-CDs and Ag+; however, the addition of GSH can significantly increase GF-CD-Ag+ fluorescence. Because of their combination with Ag+ and GSH, GF-CDs show selective fluorescence recovery. GF-CDs can serve as fluorescent probes for GSH detection. This detection method covered a wide linear range (1.6-36.0 μg mL-1) with the lowest detection limit of 0.77 μg mL-1 and manifested great advantages such as a short analysis time, good stability, repeatability, and ease of operation.

Abstract C132: SGN-35T: A novel CD30-directed antibody-drug conjugate for the treatment of lymphomas

Abstract Antibody-drug conjugates (ADCs) employing the vedotin drug linker are effective anti-cancer agents in multiple indications including Hodgkin lymphoma, cervical cancer, and bladder cancer. While vedotin ADCs have demonstrated efficacy for the treatment of a wide variety of solid and hematologic cancers, some side effects, including dose-limiting neutropenia, are commonly observed. To improve the tolerability while leveraging the known activity of brentuximab vedotin, an ADC approved for the treatment of advanced classical Hodgkin lymphoma and other CD30-expressing lymphomas, alternative ADC structural components are under exploration. A novel cleavable linker containing a tripeptide molecule comprised of D-leucine-alanine-glutamate (DLAE) was developed and used to generate SGN-35T, an anti-CD30 ADC with the same mAb backbone and cytotoxic monomethyl auristatin E (MMAE) payload as brentuximab vedotin. SGN-35T was investigated for both anti-tumor activity and effects on hematopoiesis using in vitro and in vivo assays. SGN-35T displayed comparable activity to brentuximab vedotin against three lymphoma cell lines in vitro, and complete or near-complete tumor growth inhibition in five lymphoma xenograft models including a CD30-heterogeneous model. SGN-35T led to cell cycle arrest at the G2/M phase leading to apoptosis, in concordance with the established mechanism of action of MMAE. Introduction of the tripeptide linker in SGN-35T maintained the induction of immunogenic cell death hallmarks observed with brentuximab vedotin and other vedotin-based ADCs. SGN-35T demonstrated reduced potency on hematopoiesis compared to brentuximab vedotin in a human bone marrow colony-forming unit assay. In cynomolgus monkey toxicity studies, administration of SGN-35T had a reduced impact to neutrophils counts at matched dose levels and a two-fold improvement in tolerability compared to brentuximab vedotin, with a highest non-severely toxic dose (HNSTD) of 6 mg/kg versus an HNSTD of 3 mg/kg for brentuximab vedotin when administered Q3Wx4. Together, these data demonstrate that SGN-35T exhibits anti-tumor activity in preclinical models and may reduce the severity of hematopoietic toxicities while retaining anti-tumor activity observed with brentuximab vedotin. A Phase 1, first-in-human study is planned to evaluate the safety and anti-tumor activity of SGN-35T in lymphoid malignancies. Citation Format: Kevin J Hamblett, Steven Jin, Roma Yumul, Yufei Chen, John Kwon, Jessica Simmons, Clark Henderson, Hao Sun, Jason P Schrum, Andrea R Lim, Noah A Bindman, Melissa Conerly, Astrid Clarke. SGN-35T: A novel CD30-directed antibody-drug conjugate for the treatment of lymphomas [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C132.

Эффекты пептида GHК и его структурных аналогов D-Ala-GHK и GHК-D-Ala на состояние врожденного иммунитета и перекисного окисления липидов в условиях кожной раны

Objective: to study the effects of the GHK peptide and its structure analogues on the mechanisms of innate immunity and lipid peroxidation in wound. Materials and methods. The experiments were performed on 70 male Wistar rats. The skin wound was modeled by applying a full-layer wound with an area of 250 mm2 on the animal's back. The peptides Gly-His-Lys (GHK), D-Ala-Gly-His-Lys (D-Ala-GHK), and Gly-His-Lys-D-Ala (GHK-D-Ala) were used in doses of 0.5 μg/kg and 1.5 μg/kg, which it was administered intradermally in doses of 0.5 μg/kg and 1.5 μg/kg in a volume of 0.1 ml for 3, 7 or 10 days. The activity of lipid peroxidation (LPO) processes in blood serum was assessed by the content of malonic dialdehyde (MDA) and acylhydroperoxides (AHP). The antioxidant mechanisms were evaluated by determining the activity of catalase and the total antioxidant activity (OAA) of blood serum. Phagocytic activity of blood neutrophils was assessed by phagocytic index (PI) and phagocytic number (PN). The activity of oxygen-dependent mechanisms in phagocytes was evaluated in a spontaneous nitroblue tetrazolium test (NBT). Results. After the administration of GHK, the tendency to PI, PN and completeness of phagocytosis prevailed, which mainly persisted with the use of peptides D-Ala-GHK and GHK-D-Ala. At the same time, the GHK-D-Ala peptide at a dose of 1.5 μg/kg had the most stable effect on phagocytic activity. The data obtained in the NBT are largely consistent with the PN indicators. At the same time, the effects of structural analogues, unlike GHK, were manifested throughout the experiment. Significantly significant changes in the activity of LPO and antioxidant mechanisms were observed with the use of all peptides. However, their dynamics, orientation and severity throughout the experiment were quite complex. Conclusion. GHK and its structural analogues, D-Ala-GHK and GHK-D-Ala, had an effect on the indicators of innate immunity and LPO in a skin wound, the severity and direction of which depends on the healing period. At the same time, the most pronounced and stable effects were observed when using GHK-D-Ala. That demonstrates the importance of protecting the tripeptide molecule from the action of carboxypeptidases.

Возможный механизм лиганд-рецепторного связывания синтетического трипептида Ac-RRR-NH2 с мембраной ноцицептивного нейрона

The article reports the discovery of a novel signaling cascade opioid-like receptor → Na,K-ATPase/Src → NaV1.8 channel in the nociceptive neuron membrane. Triggering this cascade results in the modulation of its effector unit—the NaV1.8 channel activation gating device, whereas the Na,K-ATPase/Src complex performs the signal transducer function. The cascade has three targets. Their modulation by the attacking molecules may evoke an antinociceptive response at the peripheral level. The first target is the opioid-like receptor activated by a number of gamma-pyrone derivatives. The second target is the Na,K-ATPase/Src complex, with its transducer function controlled by ouabain at nanomolar (endogenous) concentrations. The third target is the NaV1.8 channel activation gating device modulated by arginine-containing short peptides. The article discusses a possible mechanism of ligand-receptor binding of the arginine-containing tripeptide Ac-RRR-NH2 to the NaV1.8 channel in the primary sensory neuron membrane. Extracellular application of the tripeptide is shown by the patch-clamp method to decrease the voltage sensitivity of NaV1.8 channels. Positively charged guanidinium groups of arginine side chains are supposed to play the key role in the ligand-receptor complex formation. The results of conformational analysis demonstrate that the distances between the guanidinium groups in the tripeptide molecule exceed 10 Å. The obtained data lead us to conclude that the studied tripeptide can bind to the NaV1.8 channel using the mechanism described earlier for a range of other short arginine-containing peptides. In view of the foregoing, the tripeptide Ac-RRR-NH2 is a promising analgesic.

Copper Oxide Nanoparticle-Based Immunosensor for Zearalenone Analysis by Combining Automated Sample Pre-Processing and High-Throughput Terminal Detection.

A rapid and high-throughput fluorescence detection method for zearalenone (ZEN) based on a CuO nanoparticle (NP)-assisted signal amplification immunosensor was developed using an automated sample pretreatment and signal conversion system. CuO NPs with high stability and biocompatibility were used as carriers to immobilize anti-ZEN antibodies. The obtained CuO NP-anti-ZEN can maintain the ability to recognize target toxins and act as both a signal source and carrier to achieve signal conversion using automated equipment. In this process, target toxin detection is indirectly transformed to Cu2+ detection because of the large number of Cu2+ ions released from CuO NPs under acidic conditions. Finally, a simple and high-throughput fluorescence assay based on a fluorescent tripeptide molecule was employed to detect Cu2+, using a multifunctional microporous plate detector. A good linear relationship was observed between the fluorescence signal and the logarithm of ZEN concentration in the range of 16.0–1600.0 μg/kg. Additionally, excellent accuracy with a high recovery yield of 99.2–104.9% was obtained, which was concordant with the results obtained from LC-MS/MS of naturally contaminated samples. The CuO NP-based assay is a powerful and efficient screening tool for ZEN detection and can easily be modified to detect other mycotoxins.

The role of Fas-associated phosphatase 1 in leukemia stem cell persistence during tyrosine kinase inhibitor treatment of chronic myeloid leukemia.

Chronic myeloid leukemia (CML) is characterized by expression of Bcr-abl, a tyrosine kinase oncogene. Clinical outcomes in CML were revolutionized by development of Bcr-abl-targeted tyrosine kinase inhibitors (TKIs), but CML is not cured by these agents. CML leukemia stem cells (LSCs) are relatively TKI insensitive and persist even in remission. LSC persistence results in relapse upon TKI discontinuation, or drug resistance or blast crisis (BC) during prolonged treatment. We hypothesize that increased expression of Fas-associated phosphatase 1 (Fap1) in CML contributes to LSC persistence and BC. As Fap1 substrates include Fas and glycogen synthase kinase-3β (Gsk3β), increased Fap1 activity in CML is anticipated to induce Fas resistance and stabilization of β-catenin protein. Resistance to Fas-induced apoptosis may contribute to CML LSC persistence, and β-catenin activity increases during BC. In the current study, we directly tested the role of Fap1 in CML LSC persistence using in an in vivo murine model. In TKI-treated mice, we found that inhibiting Fap1, using a tripeptide or small molecule, prevented TKI resistance, BC and relapse after TKI discontinuation; all events observed with TKI alone. In addition, Fap1 inhibition increased Fas sensitivity and decreased β-catenin activity in CD34(+) bone marrow cells from human subjects with CML. Therapeutic Fap1 inhibition may permit TKI discontinuation and delay in progression in CML.

Anxiolytic effects of Gly-His-Lys peptide and its analogs.

Intraperitoneal administration of tripeptide Gly-His-Lys to male rats in doses of 0.5, 5, and 50 μg/kg 12 min before the start of the experiment produced an anxiolytic effect in the elevated plus maze test manifested in an increase in the time spent in open arms and shortened time spent in the closed arms. The anxiolytic effect was most pronounced after injection of 0.5 μg/kg peptide and decreased with increasing the dose of the peptide. Replacement of L-lysine with D-lysine in the tripeptide molecule was accompanied by a significant weakening of the neurotropic effects in all studied doses. Attachment of D-alanine to N- or C-terminus of Gly-His-Lys peptide leveled its anxiolytic action in all doses; significant changes in some measures of increased anxiety after administration at 50 μg/kg were found.

Adaptive spectral clustering with application to tripeptide conformation analysis

A decomposition of a molecular conformational space into sets or functions (states) allows for a reduced description of the dynamical behavior in terms of transition probabilities between these states. Spectral clustering of the corresponding transition probability matrix can then reveal metastabilities. The more states are used for the decomposition, the smaller the risk to cover multiple conformations with one state, which would make these conformations indistinguishable. However, since the computational complexity of the clustering algorithm increases quadratically with the number of states, it is desirable to have as few states as possible. To balance these two contradictory goals, we present an algorithm for an adaptive decomposition of the position space starting from a very coarse decomposition. The algorithm is applied to small data classification problems where it was shown to be superior to commonly used algorithms, e.g., k-means. We also applied this algorithm to the conformation analysis of a tripeptide molecule where six-dimensional time series are successfully analyzed.

Preparation of Nuclear Spin Singlet States Using Spin-Lock Induced Crossing

We introduce a broadly applicable technique to create nuclear spin singlet states in organic molecules and other many-atom systems. We employ a novel pulse sequence to produce a spin-lock induced crossing (SLIC) of the spin singlet and triplet energy levels, which enables triplet-singlet polarization transfer and singlet-state preparation. We demonstrate the utility of the SLIC method by producing a long-lived nuclear spin singlet state on two strongly coupled proton pairs in the tripeptide molecule phenylalanine-glycine-glycine dissolved in D(2)O and by using SLIC to measure the J couplings, chemical shift differences, and singlet lifetimes of the proton pairs. We show that SLIC is more efficient at creating nearly equivalent nuclear spin singlet states than previous pulse sequence techniques, especially when triplet-singlet polarization transfer occurs on the same time scale as spin-lattice relaxation.

UV irradiation study of a tripeptide isolated in an argon matrix: A tautomerism process evidenced by infrared and X-ray photoemission spectroscopies

Matrix isolation is a powerful tool for studying photochemical processes occurring in isolated molecules. In this way, we characterized the chemical modifications occurring within a tri peptide molecule, IGF, when exposed to the influence of Ultraviolet (UV) irradiation. This paper first describes the successful formation of the tripeptide (IGF) argon matrix under vacuum conditions, followed by the in situ UV irradiation and characterization of the molecular matrix reactivity after UV-irradiation. These studies have been performed by combining two complementary spectroscopic techniques, Fourier-Transform Reflexion Absorption Spectroscopy (FT-IRRAS) and X-ray Photoelectron Spectroscopy (XPS). The IR spectra of the isolated peptide-matrix, before and after UV irradiation, revealed significant differences that could be associated either to a partial deprotonation of the molecule or to a tautomeric conversion of some amide bonds to imide ones on some peptide molecules. XPS analyses undoubtedly confirmed the second hypothesis; the combination of IRRAS and XPS results provide evidence that UV irradiation of peptides induces a chemical reaction, namely a shift of the double bond, meaning partial conversion from amide tautomer into an imidic acid tautomer.

Transgenic rice overexpressing the Brassica juncea gamma-glutamylcysteine synthetase gene enhances tolerance to abiotic stress and improves grain yield under paddy field conditions

Glutathione (GSH), a low-molecular-weight tripeptide molecule that plays an important role in cell function and metabolism as an antioxidant, is synthesized by γ-glutamylcysteine synthetase and glutathione synthetase. To investigate the functional role of GSH in the adaptation of plants to abiotic stresses, we developed Brassica juncea L. ECS (BrECS)-expressing transgenic rice plants (BrECS1 and BrECS2) under the regulation of a stress-inducible Rab21 promoter. BrECS1 and BrECS2 transgenic rice plants with BrECS overexpression tolerated high salinity by maintaining a cellular glutathione (GSH)/glutathione disulfide redox buffer, which prevented unnecessary membrane oxidation. BrECS1 and BrECS2 rice plants also showed lower ion leakage and higher chlorophyll-fluorescence than wild-type (WT) rice plants in the presence of methyl viologen (MV) and salt, resulting in enhanced tolerance to abiotic stresses. During germination, BrECS overexpression increased growth and development, resulting in an increased germination rate in the presence of salt conditions, but not under salt-free normal conditions. Furthermore, BrECS1 and BrECS2 rice plants displayed a moderate increase in biomass and rice grain yield under general paddy field conditions when compared to WT rice plants under general paddy field conditions. Therefore, our results suggest that BrECS-overexpression was critical for cellular defense from reactive oxygen species attacks produced by salt and MV, promotion of germination, and metabolic processes involved in natural environmental stress tolerance, thereby enhancing growth development and rice grain yield.

NNZ-2566: A Gly–Pro–Glu analogue with neuroprotective efficacy in a rat model of acute focal stroke

The N-terminal cleavage product of human insulin-like growth factor-1 (IGF-1) in the brain is the tripeptide molecule Glypromate ® (Gly–Pro–Glu). Glypromate ® has demonstrated neuroprotective effects in numerous in vitro and in vivo models of brain injury and is in clinical trials for the prevention of cognitive impairment following cardiac surgery. NNZ-2566 is a structural analogue of Glypromate ®, resulting from α-methylation of the proline moiety, which has improved the elimination half-life and oral bioavailability over the parent peptide. In vivo, NNZ-2566 reduces injury size in rats subjected to focal stroke. An intravenous infusion of NNZ-2566 of 4 h duration (3–10 mg/kg/h), initiated 3 h after endothelin-induced middle-cerebral artery constriction, significantly reduced infarct area as assessed on day 5. Neuroprotective efficacy in the MCAO model was also observed following oral administration of the drug (30–60 mg/kg), when formulated as a microemulsion. In vitro, NNZ-2566 significantly attenuates apoptotic cell death in primary striatal cultures, suggesting attenuation of apoptosis is one mechanism of action underlying its neuroprotective effects. NNZ-2566 is currently in clinical trials for the treatment of cognitive deficits following traumatic brain injury, and these data further support the development of the drug as a neuroprotective agent for acute brain injury.

Cathodic electrodeposition of ZnO and CuSCN thin films in the presence of glutathione

The effect of a tripeptide molecule glutathione (γ-L-glutamyl-L-cysteniylglycine, QCG) is studied as a structure-directing agents (SDA) for cathodic electrodeposition of ZnO and CuSCN from aqueous solutions, which are known to be wide bandgap semiconductors of n and p types, respectively. From experiences, hard Lewis basic –COOH group act as an anchor to the hard Lewis acidic Zn(II) sites of ZnO, whereas soft Lewis basic groups such as –SH and –NH2 are expected to interact with soft Lewis acidic Cu(I) sites of CuSCN. QCG have all these anchoring groups within its structure and was found to affect the growth of both ZnO and CuSCN, leading to alteration of crystallographic orientations and evolution of unique nanostructures.

Antibody recognition of chiral surfaces. Enantiomorphous crystals of leucine-leucine-tyrosine.

Monoclonal antibodies were selected after immunization with crystals of the tripeptide l-leucine-l-leucine-l-tyrosine. They interact with the tripeptide crystals, but do not interact with the tripeptide molecule, with other crystalline surfaces, or with adsorbed protein. The interactions of two antibodies with crystals of l-Leu-l-Leu-l-Tyr and of its enantiomer d-Leu-d-Leu-d-Tyr were characterized in depth. Antibody 48E is stereoselective and enantioselective: it recognizes only the [011] faces of the l-Leu-l-Leu-l-Tyr crystals, and not the enantiomorphous [011] faces of d-Leu-d-Leu-d-Tyr crystals, or any other faces of either crystal. In contrast, antibody 602E is poorly stereoselective and is not enantioselective: it recognizes the crystals of both enantiomers, interacting with a number of different faces of each. The different recognition patterns are explained on the basis of the nature of the interactions and the structure of the interacting surfaces. Understanding this antibody specificity advances our general understanding of surface recognition and transfer of chiral information across biological interfaces.

Crystal structure of the complex of concanavalin A and tripeptide.

The X-ray structure analysis of a cross-linked crystal of concanavalin A soaked with the tripeptide molecule as the probe molecule showed electron density corresponding to full occupation in the binding pocket. The site lies on the surface of concanavalin A and is surrounded by three symmetry-related molecules. The crystal structure of the tripeptide complex was refined at 2.4-A resolution to an R-factor of 17.5%, (Rfree factor of 23.7%), with an RMS deviation in bond distances of 0.01 A. The model includes all 237 residue of concanavalin A, 1 manganese ion, 1 calcium ion, 161 water molecules, 1 glutaraldehyde molecule, and 1 tripeptide molecule. This X-ray structure analysis also provides an approach to mapping the binding surface of crystalline protein with a probe molecule that is dissolved in a mixture of organic solvent with water or in neat organic solvent but is hardly dissolved in aqueous solution.

Glutathione modulates the [formula omitted] receptor-activated calcium influx into cultured rat cerebellar granule cells

The effects of reduced (GSH) and oxidized (GSSG) glutathione and dithiothreitol (DTT) and l-cysteine on the influx of 45Ca 2+ were studied with cultured cerebellar granule cells. DTT slightly enhanced the basal influx but strongly activated the influx stimulated by glutamate or N- methyl- d-aspartate (NMDA). The effects on the kainate- or quisqualate-induced influx were less pronounced. Extracellular GSH had no effect on the basal influx of Ca 2+. A concentration of 0.5 mM GSH slightly activated the glutamate- and NMDA-induced influx while GSSG was inhibitory. The enhancement by DTT and cysteine of the responses to excitatory amino acids was attenuated by GSH and GSSG. We propose that both the accessibility and redox state of the functional sulfhydryl groups in NMDA receptor-ionophores may be regulated by endogenous glutathione. These effects are attributed to the γ-glutamyl moiety and sulfhydryl group in the tripeptide molecule.

Effects of tripeptides derived from milk proteins on polymorphonuclear oxidative and phosphoinositide metabolisms

The tripeptide GLF (glycyl-leucyl-phenylalanine) was isolated from human milk proteins. This peptide increased phagocytosis by human and murine macrophages and protected mice against Klebsiella pneumonia infection. Specific binding sites on human polymorphonuclear leukocytes (PMNs) have been demonstrated recently. The aim of the present research was to study the action of this peptide on rat and human PMN oxidative burst and to investigate the consequences of cell stimulation on polyphosphoinositide hydrolysis. A biphasic stimulating concentration-dependent effect of GLF on PMN chemiluminescence and Superoxide anion generation was demonstrated. One of the peaks of the oxidative response occurred around 10 −9 M, which correlates with the K d of high affinity receptors of GLF. The other maximum, around 10 −4 M, might be due to the hydrophobic nature of the tripeptide. O − 2 generation mimicked the phorbol myristate acetate response: after a lag period of 2–5 min. O − 2 release gradually increased for 10–15 min until a plateau was reached. Furthermore, GLF enhanced phosphoinositide breakdown with maximal IP 3 production at 10 −7 M. Various analogs of GLF were synthesized in order to define the relative importance of the different amino acids and their position in the tripeptide molecule: glycyl-phenylalanine-leucine was devoid of biological properties but enhanced the activity of GLF on the metabolic burst at high concentrations; peptides leucyl-leucyl-phenylalanine and leucyl-leucyl-tyrosine, which displaced GLF from its specific membrane receptors, exerted stimulating effects on PMN oxidative and phosphoinositide metabolisms. It is quite conceivable that these short peptides, which may be generated in the newborn during digestion and which are able to stimulate phagocytic cells, are implicated in the defense of the neonate immature organism against infection.

Helix-forming tendencies of amino acids depend on the restrictions of side-chain rotamer conformations: crystal structure of the tripeptide GAI in two crystalline forms.

In our attempts to design crystalline alpha-helical peptides, we synthesized and crystallized GAI (C11H21N3O4) in two crystal forms, GAI1 and GAI2. Form 1 (GAI1) Gly-L-Ala-L-Ile (C11H21N3O4.3H2O) crystals are monoclinic, space group P2(1) with a = 8.171(2), b = 6.072(4), c = 16.443(4) A, beta = 101.24(2) degrees, V = 800 A3, Dc = 1.300 g cm-3 and Z = 2, R = 0.081 for 482 reflections. Form 2 (GAI2) Gly-L-Ala-L-Ile (C11H21N3O4.1/2H2O) is triclinic, space group P1 with a = 5.830(1), b = 8.832(2), c = 15.008(2) A, alpha = 102.88(1), beta = 101.16(2), gamma = 70.72(2) degrees, V = 705 A3, Z = 2, Dc = 1.264 g cm-3, R = 0.04 for 2582 reflections. GAI1 is isomorphous with GAV and forms a helix, whereas GAI2 does not. In GAI1, the tripeptide molecule is held in a near helical conformation by a water molecule that bridges the NH3+ and COO- groups, and acts as the fourth residue needed to complete the turn by forming two hydrogen bonds. Two other water molecules form intermolecular hydrogen bonds in stabilizing the helical structure so that the end result is a column of molecules that looks like an incipient alpha-helix. GAI2 imitates a cyclic peptide and traps a water molecule. The conformation angles chi 11 and chi 12 for the side chain are (-63.7 degrees, 171.1 degrees) for the helical GAI1, and (-65.1 degrees, 58.6 degrees) and (-65.0 degrees, 58.9 degrees) for the two independent nonhelical molecules in GAI2; in GAI1, both the C gamma atoms point away from the helix, whereas in GAI2 the C gamma atom with the g+ conformation points inward to the helix and causes sterical interaction with atoms in the adjacent peptide plane. From these results, it is clear that the helix-forming tendencies of amino acids correlate with the restrictions of side-chain rotamer conformations. Both the peptide units in GAI1 are trans and show significant deviation from planarity [omega 1 = -168(1) degrees; omega 2 = -171(1) degrees] whereas both the peptide units in both the molecules A and B in GAI2 do not show significant deviation from planarity [omega 1 = 179.3(3) degrees; omega 2 = -179.3(3) degrees for molecule A and omega 1 = 179.5(3) degrees; omega 2 = -179.4(3) degrees for molecule B], indicating that the peptide planes in these incipient alpha-helical peptides are considerably bent.

Oxygen free radicals and myocardial damage: Protective role of thiol-containing agents

It has been suggested that the sudden presence of oxygen during reperfusion after a period of ischemia may be toxic for the myocardial cell. The oxygen molecule is capable of producing reactions in the cell, forming highly reactive free radicals, and inducing lipid peroxidation of membranes, altering their integrity and increasing their fluidity and permeability. The ischemic and reperfused cardiac cell is the prime candidate for this reaction sequence and may explain the molecular mechanism underlying the pathologic events related to membrane dysfunction and calcium homeostasis. However, the myocardium has a series of defense mechanisms including the enzymes superoxide dismutase (SOD), catalase, and glutathione peroxidase plus other endogenous antioxidants such as vitamin E, ascorbic acid, and cysteine to protect the cell against the cytoxic oxygen metabolites. The prerequisite for oxygen free radical involvement in ischemia and reperfusion damage is that ischemia alters the defense mechanisms against oxygen toxicity. It is known that ischemia may impair mitochondrial SOD and, with reperfusion, oxidative stress may occur as shown by tissue accumulation and release of oxidized glutathione. This tripeptide molecule is the cofactor of glutathione peroxidase, the enzyme that removes hydrogen and lipid peroxides. Its formation and subsequent release is a reliable index of oxidative damage. In our study, we investigated the effects of N-acetylcysteine on oxidative damage in the isolated rabbit heart. N-acetylcysteine increases, in a dose-dependent manner (from 10 −7 to 10 −5 M), the myocardial glutathione content and provides an important degree of protection against ischemia and reperfusion. Oxidative stress does not occur, mitochondrial function is maintained, enzyme release is reduced, and contractile recovery is increased. Similarly, we administered N-acetylcysteine in the pulmonary artery of coronary artery disease patients undergoing coronary bypass grafting (150 mg/kg in 1 hour followed by 150 mg/kg in 4 hours). The degree of oxidative stress on reperfusion was reduced and recovery of cardiac function improved. In this article, we review the cardioprotective role of thiol-containing agents.