Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “AMIDES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17Linked to original sources
PubMed2006

Extended application of a chiral stationary phase based on (+)-(1 8-crown-6)-2,3,11,12-tetracarboxylic acid to the resolution of N-(substituted benzoyl)-alpha-amino acid amides.

A chiral stationary phase (CSP 1) based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid was applied to the resolution of N-(substituted benzoyl)-alpha-amino acid amides and esters. N-(Substituted benzoyl)-alpha-amino acid amides were well resolved using a mixture of acetic acid-triethylamine-acetonitrile (0.01:0.05:100, v/v/v) as an optimum mobile phase while N-(substituted benzoyl)-alpha-amino acid esters were not resolved at all. In contrast, both N-(substituted benzoyl)-alpha-amino acid amides and esters were not resolved at all or resolved very poorly on another CSP (CSP 2), which lacks the two N-H hydrogens of the amide tethers of CSP 1. Among the substituents on the benzoyl group of analytes, the nitro group was the best for good resolution of analytes on CSP 1. From these results, the two N-H hydrogens of the amide tethers of CSP 1, the carbonyl oxygen of the amide group of analytes, and the nitro group on the benzoyl group of analytes were concluded to play significant roles in chiral recognition. In addition, various N-(3,5-dinitrobenzoyl)leucine amides with different lengths of N-alkylamide chains were resolved on CSP 1 and N-(3,5-dinitrobenzoyl) leucine N-propylamide was found to show the best chiral recognition in terms of the separation (alpha = 1.30) and the resolution factor (Rs= 3.17).

Amides↗
PubMed2002

Studying protein-carbohydrate interactions by amide hydrogen/deuterium exchange mass spectrometry.

Protein-carbohydrate interactions play a significant role in biological processes. Presented here is the novel application of amide hydrogen/deuterium exchange mass spectrometry (amide exchange-MS) to the study of the interaction between a protein and its carbohydrate substrate. The degree of deuterium incorporation into hen egg lysozyme was monitored with and without substrate to verify that a carbohydrate can provide sufficiently stable protection of the amide hydrogen atoms in a protein's backbone from exchange with deuterated solvent. The substrate protected a number of amide hydrogens from exchange, implying that protein-carbohydrate binding systems will be compatible with amide exchange-MS. Endopolygalacturonase-II (EPG-II) from Aspergillus niger, a pectin-degrading enzyme, was chosen as the first carbohydrate-binding system to be extensively studied using quenched amide exchange-MS. Monitoring the changes in deuterium incorporation of EPG-II in the presence and absence of an oligomer of galacturonic acid implied the location of substrate binding. This study demonstrates the ability of amide exchange-MS to investigate protein-carbohydrate interactions.

Amides↗
PubMed1993

FTIR spectroscopic analysis of the amide and acid bands of ganglioside GM1, in pure form and in mixtures with DMPC.

The amide I bands of sphingolipids show complicated patterns due to intra- and intermolecular interactions via hydrogen bonds. In order to assign the amide I absorption bands of the ganglioside GM1 to the different amide groups in the headgroup and back bone, the compounds N-acetylgalactosamine, N-acetylneuraminic acid, glucocerebroside and ceramide III were examined as reference systems. The frequencies of the COOH and COO- bands of the sialic acid residue of GM1 were determined by pH-titration and were found to absorb at 1729 cm-1 and 1605 cm-1, respectively. In D2O the three amide groups of GM1 give one broad absorption band at 1627 cm-1, whereas in the glucocerebroside intra- and intermolecular interactions of the amide group give rise to three distinct amide I bands. For a solid sample of GM1 in KBr also one broad band was observed in the amide I region. We also studied the influence of the ganglioside GM1 on model membranes of DMPC as host lipid. The change of the CH2 stretching vibrational absorption bands as a function of temperature reveal that addition of GM1 to DMPC leads to increased phase transition temperatures Tm with increasing ganglioside content. No Ca2+ binding to the COO- group of GM1 was observed.

Acetylgalactosamine↗
PubMed1976

Amidated carboxyl groups in elastin.

Dicarboxylic amino acids constitute the most numerous residues of insoluble elastin in which are potentially ionizable in the physiological range of pH. These residues are essential in facilitating productive electrostatic interaction between elastase and elastin. The present study has investigated the possibility that the glutamic and aspartic acid residues of elastin are amidated. Acid-labile amide-bound ammonia of elastin was quantitated after hydrolysis of the insoluble protein with 2 M HC1 by incubating aliquots of microdistilled hydrolysates with glutamate dehydrogenase, excess alpha-ketoglutarate, and reduced nicotinamide adenine dinucleotide and measuring the resultant decrease in A340 due to oxidation of the dinucleotide cofactor. It was found that ligament elastin purified by repeated autoclaving contains approximately 2.29 mumol of acid-labile amide nitrogen per 10 mg of protein, a value equivalent to approximately 70% of the total number of dicarboxylic amino acid residues. Independent analysis of the amide content was obtained by amino acid analysis of an esterified and reduced elastin sample in which the free dicarboxylic amino acid residues had been converted to the corresponding alcohol derivatives. This analysis indicated that autoclaved ligament elastin contains approximately 18 glutamine, 3 asparagine, 4 glutamic acid and 5 aspartic acid residues per 1000 residues, in good agreement with the analysis of total acid-labile ammonia. The esterified and reduced elastin derivative was nearly inert as an elastase substrate, consistent with a lack of free dicarboxylic amino acid residues. However, addition of sodium dodecyl sulfate to this elastin derivative restores enzyme-substrate charge complementarity, and the elastin-ligand complex was readily hydrolyzed by elastase at the fully stimulated rate, emphasizing the control such ligands can exert in elastolysis. The amide bonds of elastin were found to be significantly more resistant to hydrolysis by 0.1 M NaOH at 98 degrees C than were those of lysozyme or free amidated amino acids. The finding that most of dicarboxylic amino acid residues of elastin exist at neutral amides further emphasizes the apolar character of elastin and has bearing upon the metabolic susceptibility, ligand-binding ability and structural aspects of this connective tissue protein.

Amides↗
PubMed1983

The amidating enzyme in pituitary will accept a peptide with C-terminal D-alanine as substrate.

A series of tripeptides which terminated in d-alanine, d-serine, d-leucine or l-alanine was synthesized and the peptides tested for their ability to act as substrates for an amidating enzyme present in porcine pituitary. The peptides were allowed to compete with a radiolabelled substrate 125I d-Tyr Phe Gly in the presence of a rate limiting concentration of amidating enzyme and the degree of conversion to 125I d-Tyr Phe amide was determined by ion exchange chromatography. An accelerated procedure was developed for investigating the rates of reaction. The results showed that d-Tyr Phe d-Ala has a significant affinity for the amidating enzyme; no affinity could be demonstrated with d-Tyr Phe 1-Ala, d-Tyr Phe d-Ser or d-Tyr Phe d-Leu. Direct evidence that d-Tyr Phe d-Ala can undergo amidation was obtained by incubating the 125I labelled tripeptide with the pituitary enzyme. Amidation took place readily with d-Tyr Phe d-Ala but not with the other tripeptides; thus, while the enzyme is unable to catalyse the conversion of a peptide terminating in 1-alanine, it can accept a peptide terminating in d-alanine. The results indicate that the amidating enzyme has a highly compact substrate binding site.

Alanine↗
PubMed1990

Alpha-amidation of gastrin is impaired by diethyldithiocarbamate.

The influence of gastrin alpha-amidation of the heavy-metal chelator diethyldithiocarbamate and disulfiram, its disulfide dimer, was studied in rat gastric antrum. Sensitive, sequence-specific immunoassays for glycine-extended and amidated gastrin were used to monitor extractions and chromatography. The results showed that intraperitoneal diethyldithiocarbamate administration (1000 mg/kg body weight) for two days caused a decrease in amidated gastrin from 2.6 +/- 0.4 to 1.4 +/- 0.3 nmol/g tissue (n = 11) with a simultaneous increase in glycine-extended gastrin from 0.84 +/- 0.15 to 2.4 +/- 0.3 nmol/g. Peroral administration of disulfiram (4 mg/kg body weight) for nine days did not change alpha-amidation significantly. The results of the present study demonstrate that the heavy-metal chelating agent diethyldithiocarbamate inhibits alpha-amidation of gastrin in vivo, in agreement with the inhibition of amidating activity observed in vitro. These results are in accordance with the previous observations that the presence of copper ions is necessary for the alpha-amidation to take place.

Amides↗
PubMed1994

Enantioselective hydrolysis of racemic naproxen nitrile and naproxen amide to S-naproxen by new bacterial isolates.

Bacteria were enriched from soil samples with succinate as a carbon source and racemic naproxen nitrile [2-(6-methoxy-2-naphthyl)propionitrile] as sole source of nitrogen. Since naproxen nitrile was only poorly soluble in water media amended with different water-immiscible organic phases were used for the enrichments. With pristane (2,6,10,14-tetramethylpentadecane) as the organic phase two bacterial strains were isolated (strain C3II and strain MP50) which were identified as rhodococci. Cells of both strains converted naproxen nitrile via naproxen amide to naproxen. From racemic naproxen nitrile Rhodococcus sp. C3II formed S-naproxen amide and subsequently S-naproxen. Racemic naproxen amide was hydrolysed to S-naproxen. Rhodococcus sp. MP50 converted racemic naproxen nitrile predominantly to R-naproxen amide and racemic naproxen amide to S-naproxen. With both strains racemic naproxen amide was converted to S-naproxen with an enantiomeric excess > 99% at a conversion rate up to 80% of the theoretical value. In strain C3II the enzymes which hydrolysed naproxen nitrile and naproxen amide were present only at a low constitutive level. In contrast, in Rhodococcus sp. MP50 these activities were induced when grown in the presence of various nitriles.

Amides↗
PubMed1994

Tilted amides in amino acid and peptide derivatives.

BACKGROUND: Amide bonds in peptides and proteins typically adopt planar cis or trans conformations. Conversions between cis and trans amide conformations are necessary for protein folding and for many other processes, but are difficult to achieve since they involve disruption of the planarity of the bond. As a first step to understanding cis-trans isomerization, we set out to synthesize and characterize peptides that mimic the tilted or twisted amide structures that are postulated to form the intermediate states in this process. RESULTS: We have synthesized a model amino acid and four dipeptide derivatives containing a methyl-substituted aziridine residue. Single crystals of phenacyl (2R, 3R)-benzyloxycarbonyl-3-methyl-2-aziridinecarboxylate and phenacyl (2R, 3R)-acetyl-glycyl-3-methyl-2-aziridine-carboxylate were obtained. Using X-ray diffraction analysis, we determined that the amide nitrogens of the aziridine rings have tetrahedral sp3-like geometry with tilt angles in the range of 37-38 degrees. The 13C-NMR spectra indicate that the amide carbonyl is dramatically shifted downfield as a consequence of the tilt. CONCLUSIONS: In peptides containing a substituted aziridine ring, the orbitals of the amide nitrogen are constrained into a tilted configuration. These peptides may mimic the transition state between cis and trans amide conformations. This technique thus provides a novel strategy for the study of isomerization and other biorecognition processes.

Amides↗
PubMed2005

Small angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) studies of amide phospholipids.

Varying chemically the structure of phospholipids in the region between hydrophobic and hydrophilic segments is expected to have a strong influence on the interaction with water and the phase behavior. This is studied in this work with the motivation to investigate these lipids as potential inhibitors of phospholipase A2. Thus the amide phospholipids L-ether-amide-PC (1-O-hexadecyl-2-N-palmitoyl-2-amino-2-deoxy-sn-glycero-3-phosphocholine), L-ester-amide-PC (1-palmitoyl-2-N-palmitoyl-2-amino-2-deoxy-sn-glycero-3-phosphocholine) and L-ether-amide-PE (1-O-hexadecyl-2-N-palmitoyl-2-deoxy-sn-glycero-3-phosphoethanolamine) have been synthesized and characterized. The phase behavior and thermal transitions in buffer dispersions are examined by a combination of high-sensitivity differential scanning calorimetry (DSC) and small angle X-ray scattering (SAXS) experiments between 10 and 80 degrees C at pH 8.9. The onset temperatures determined from DSC measurements agree well with the starting temperatures of changes in the repeat distance obtained by SAXS measurements. The phases observed are lamellar both below and above the main phase transition. The phase transition temperatures and enthalpies depend strongly on the substitutions in sn-1 position and head group structure. The lamellar repeat distance in gel and liquid-crystalline phases increases with increasing temperature for L-ester-amide-PC and L-ether-amide-PC, whereas the temperature dependence is opposite for the L-ether-amide-PE. The observed behavior is discussed and compared with that of DPPC and DPPE, indicating the strong dependence of hydration and phase behavior on head group structure.

Amides↗
PubMed1986

Resolution of enantiomeric amides on a cellulose-based chiral stationary phase. Steric and electronic effects.

A series of enantiomeric amides were resolved on a commercially available chiral stationary phase (CSP) consisting of cellulose tribenzoate coated on macroporous silica. The amides were synthesized from several homologous series of aliphatic and aromatic chiral amines and a series of aliphatic chiral acids. The results of the study indicate that the formation of the solute-CSP diastereomeric complex is based on a combination of hydrogen bonding, pi-pi and amide dipole interactions. These interactions not only form the diastereomeric complex but also appear to position the solute and CSP within the complex. This is suggested by the fact that the enantiomeric elution order for a series of amides formed from aliphatic amines is R, S, whereas the enantiomeric elution order for the corresponding series of amides formed from aliphatic acids is S, R. The effects of steric bulk at the chiral center were also investigated; the results indicate that for the homologous series of aliphatic amides, an increase in the length of the alkyl chain attached to the chiral center results in an increase in the chiral resolution (alpha). This is not the case, however, for the homologous series of aromatic amides; the results suggest that chiral recognition is a function of the fit of the asymmetric portion of the solute in a chiral cavity (or channel) of the CSP and that this fit has rigid steric requirements.

Amides↗
PubMed1986

Resolution of enantiomeric amides on a Pirkle-type chiral stationary phase. A comparison of subcritical fluid and liquid chromatographic approaches.

Subcritical and supercritical fluid chromatography (SubFC and SFC) have been evaluated for the resolution of an homologous series of enantiomeric amides. The solutes were the 2-naphthoyl amides of an homologous series of amines, ranging from 2-aminobutane to 2-aminoctane, and the p-methyl-, p-methoxy- and p-chlorophenylamides of 2-aminoheptane. The chiral stationary phase (CSP) used was the covalent form of (R)-N-(3,5-dinitrobenzoyl)phenylglycine. In liquid chromatography (LC) the mobile phase comprised hexane-2-propanol--acetonitrile (97:3:0.5) at a flow-rate of 2 ml/min and temperatures of 20-35 degrees C. In SFC, the mobile were various mixtures of carbon dioxide and polar modifiers, such as alcohols, chloroform and water. For the best conditions in LC, the chiral resolution, alpha, increased through the homologous series from alpha = 1.03 for the amide derived from 2-aminobutane to alpha = 1.11 for the 2-aminooctane amide. The values of alpha observed for the pi-basic amides of 2-aminoheptane (p-methyl and p-methoxy) were greater than that observed for the pi-acidic amide (p-chloro), i.e., alpha = 1.08 versus 1.04. The selectivities, resolutions and efficiencies obtained by LC and SubFC were similar. These results indicate that the mechanism of chiral recognition is the same in LC and SubFC and that the methods should be interchangeable. The actual analysis time for SubFC was significantly shorter than that required for LC: as short as 2 min for the 2-aminooctane amide, whereas LC takes over 10 min under the best conditions.

Amides↗
PubMed1999

Determination of fatty acid amides as trimethylsilyl derivatives by gas chromatography with mass spectrometric detection.

Fatty acid amides are a newly emerging class of compounds with biological activity. The amides are formed enzymatically in vivo. Analysis of fatty acid amides has been accomplished by gas chromatography coupled with mass spectrometry. Fatty acid amides required derivatization prior to analysis at high temperatures due to thermal instability. Trimethylsilylation of fatty acid amides has been accomplished under optimum reaction conditions. The limit of detection for the silylated amides is approximately 1 pmol, with the lowest detected level being 700 fmol for the lauramide derivative. Quantitation of fatty acid amide derivatives can be accomplished by monitoring m/z 59 or m/z M-71, the only two major fragments formed in the ion trap mass spectrometer with electron impact ionization. The smaller fragment is the result of a newly reported, McLafferty-type rearrangement; M-71 resulted from loss of an n-pentyl fragment. Either peak gave four-five orders of magnitude linear dynamic range. Numerous trimethylsilylamides from C7 to C20 were separated under standard conditions. Elution was linear with the number of carbons and was systematically affected by the number and position of the double bonds.

Amides↗
PubMed2002

Recent developments in the electronic spectroscopy of amides and alpha-helical polypeptides.

Recent experimental and theoretical advances in understanding the electronic excited states of simple amides are reviewed. Polarized reflection spectroscopy of single crystals of N-acetylglycine shows that the direction of the first pipi* (NV(1)) transition dipole moment of a secondary amide differs by approximately 15 degrees from that of a primary amide. Ab initio calculations on simple amides support this conclusion. Ab initio studies of di- and tri-amides demonstrate that several inter-amide charge-transfer (CT) transitions occur in the 150-175-nm region, between the NV(1) and NV(2) transitions. When the correct dipole transition moment direction for peptides is used in calculations of the circular dichroism of the alpha-helix, the results are much improved over those from earlier calculations that used the direction for primary amides. Studies that consider the mixing of the NV(1) transition with CT transitions are reviewed. These indicate that such mixing is likely to have a significant effect on the absorption and CD spectra of the alpha-helix and other types of peptide conformation. Nevertheless, the independent systems model gives a reasonable first approximation to the absorption and CD spectra of the alpha-helix.

Amides↗
PubMed1998

Novel antiallergic agents. Part I: Synthesis and pharmacology of pyrimidine amide derivatives.

We have synthesized many pyrimidine amide derivatives. Novel pyrimidine bis-glycolic amide derivatives showed moderate inhibition in the rat passive cutaneous anaphylaxis (PCA) assay by oral administration. Among these compounds, 2,4-bis(methoxyacetylamino)-6-piperidinopyrimidine (2i) exhibited significant inhibition. However the compound (2i) did not inhibit antigen-induced histamine or SRS-A release from lung fragments of the guinea-pig at less than 10(-4) M. Derivatives of 2i have also notable or moderate activity in the rat PCA assay. Compound 2h which has no oxygen atom at the alpha-position of the amide carbonyl group and, compound 17 which has no amide carbonyl group, showed no inhibition in the rat PCA assay. We supposed that both the amide carbonyl group and the oxygen atom at alpha-position of the amide carbonyl group play an important role in inhibiting the rat PCA reaction. These pyrimidine bis-glycolic amide derivatives have a novel structure and unique activity which suggests they may be potentially useful in the treatment of allergic diseases.

Administration, Oral↗
PubMed1988

Destruction of intracellular and isolated Leishmania mexicana amazonensis amastigotes by amino acid amides.

L-amino acid esters such as leucine methyl ester (Leu-OMe) destroy Leishmania mexicana amazonensis amastigotes by a mechanism which may involve hydrolysis of the compounds by parasite enzymes. Moreover, several esters (e.g. Ile-OMe) prevent the killing of parasites by Leu-OMe, perhaps by inhibition of the hydrolytic enzymes. We show here that certain amino acid amides are also leishmanicidal. Killing of Leishmania within macrophages was assessed microscopically, and that of isolated amastigotes was measured by reduction of the tetrazolium MTT. Amino acid amides were generally less active than the methyl esters and several were more toxic to the macrophages, as determined by inspection of Giemsa-stained preparations. Ranks of activity of the amides on isolated amastigotes were Trp greater than Leu greater than Phe greater than Met greater than Tyr. The amides of Ala, Gly, Val, Ile, His and D-Leu were inactive. This pattern of activity is similar to that of amino acid methyl esters. Ile-NH2 and a few other amides protected intracellular as well as isolated parasites from killing by Leu-OMe. Conversely, Ile-OMe reduced the toxicity of Leu-NH2 for isolated amastigotes. None of the esters or amides assayed prevented the destruction of Leishmania by Trp-NH2. The results are compatible with the view that amino acid esters and amides may be recognized by the same or similar parasite enzymes.

Amides↗
PubMed1988

Structure and dynamics of a detergent-solubilized membrane protein: measurement of amide hydrogen exchange rates in M13 coat protein by 1H NMR spectroscopy.

The coat protein of bacteriophage M13 is inserted into the inner membrane of Escherichia coli where it exists as an integral membrane protein during the reproductive cycle of the phage. The protein sequence consists of a highly hydrophobic 19-residue central segment flanked by an acidic 20-residue N-terminus and a basic 11-residue C-terminus. We have measured backbone amide hydrogen exchange of the protein solubilized in perdeuteriated sodium dodecyl sulfate using 1H nuclear magnetic resonance (NMR) spectroscopy. Direct proton exchange-out measurements in D2O at 24 degrees C were used to follow the exchange of the slowest amides in the protein. Multiple exponential fitting of the exchange data showed that these amides (29 +/- 3 at pH 4.5) exchanged in two kinetic sets with exchange rates [(1.2 +/- 0.4) x 10(-4) s-1 and (4.1 +/- 1.2) x 10(-7) s-1] that differed by more than 100-fold, the slower kinetic set being retarded 10(5)-fold relative to poly(DL-alanine). The exchange rate constant for the slowest set of amides exhibited an unusual pD dependence, being proportional to [OD-]1/2. It is shown that this is an artifact of the multiple exponential fitting of the data, and a new method of presentation of exchange data as a function of pD is introduced. Steady-state saturation-transfer techniques were also used to measure exchange. These methods showed that 15-20 amides in the protein are very stable at 55 degrees C and that about 30 amides have exchange rates retarded by at least 10(5)-fold at 24 degrees C. Saturation-transfer studies also showed that the pH dependence of exchange in the hydrophilic termini was unusual. This is explained as being due to long-range electrostatic effects arising both from the protein itself and also from the anionic detergent molecules. Hydrogen exchange studies on the products of proteinase K digestion of the protein localized the slowly exchanging amides to the hydrophobic core of the protein. Relaxation [Henry, G.D., Weiner, J.H., & Sykes, B.D. (1986) Biochemistry 25, 590-598] and solid-state NMR experiments [Leo, G.C., Colnago, L.A., Valentine, K.G., & Opella, S.J. (1987) Biochemistry 26, 854-862] have previously shown that the majority of the protein backbone is rigid on the picosecond to microsecond time scale, except for the extreme ends of the molecule which are mobile.(ABSTRACT TRUNCATED AT 400 WORDS)

Amides↗
PubMed2002

pH and urea dependence of amide hydrogen-deuterium exchange rates in the beta-trefoil protein hisactophilin.

Amide hydrogen/deuterium exchange rates were measured as a function of pH and urea for 37 slowly exchanging amides in the beta-trefoil protein hisactophilin. The rank order of exchange rates is generally maintained under different solution conditions, and trends in the pH and urea dependence of exchange rates are correlated with the rank order of exchange rates. The observed trends are consistent with the expected behavior for exchange of different amides via global and/or local unfolding. Analysis of the pH dependence of exchange in terms of rate constants for structural opening and closing reveals a wide range of rates in different parts of the hisactophilin structure. The slowest exchanging amides have the slowest opening and closing rates. Many of the slowest exchanging amides are located in trefoil 2, but there are also some slow exchanging amides in trefoils 1 and 3. Slow exchangers tend to be near the interface between the beta-barrel and the beta-hairpin triplet portions of this single-domain structure. The pattern of exchange behaviour in hisactophilin is similar to that observed previously in interleukin-1 beta, indicating that exchange properties may be conserved among beta-trefoil proteins. Comparisons of opening and closing rates in hisactophilin with rates obtained for other proteins reveal clear trends for opening rates; however, trends in closing rates are less apparent, perhaps due to inaccuracies in the values used for intrinsic exchange rates in the data fitting. On the basis of the pH and urea dependence of exchange rates and optical measurements of stability and folding, EX2 is the main exchange mechanism in hisactophilin, but there is also evidence for varying levels of EX1 exchange at low and high pH and high urea concentrations. Equilibrium intermediates in which subglobal portions of structure are cooperatively disrupted are not apparent from analysis of the urea dependence of exchange rates. There is, however, a strong correlation between the Gibbs free energy of opening and the denaturant dependence of opening for all amides, which suggests exchange from a continuum of states with different levels of structure. Intermediates are not very prominent either in equilibrium exchange experiments or in quenched-flow kinetic studies; hence, hisactophilin may not form partially folded states as readily as IL-1 beta and other beta-trefoil proteins.

Amides↗
PubMed1993

Peptide alpha-keto ester, alpha-keto amide, and alpha-keto acid inhibitors of calpains and other cysteine proteases.

A series of dipeptidyl and tripeptidyl alpha-keto esters, alpha-keto amides, and alpha-keto acids having leucine in the P2 position were synthesized and evaluated as inhibitors for the cysteine proteases calpain I, calpain II, cathepsin B, and papain. In general, peptidyl alpha-keto acids were more inhibitory toward calpain I and II than alpha-keto amides, which in turn were more effective than alpha-keto esters. In the series Z-Leu-AA-COOEt, the inhibitory potency decreased in the order: Met (lowest KI) > Nva > Phe > 4-Cl-Phe > Abu > Nle (highest KI) with calpain I, while almost the reverse order was observed for calpain II. Extending the dipeptide alpha-keto ester to a tripeptide alpha-keto ester yielded significant enhancement in the inhibitory potency toward cathepsin B, but smaller changes toward the calpains. Changing the ester group in the alpha-keto esters did not substantially decrease KI values for calpain I and calpain II. N-Monosubstituted alpha-keto amides were better inhibitors than the corresponding alpha-keto esters. alpha-Keto amides with hydrophobic alkyl groups or alkyl groups with an attached phenyl group had the lower KI values. N,N-Disubstituted alpha-keto amides were much less potent inhibitors than the corresponding N-monosubstituted peptide alpha-keto amides. The peptide alpha-keto acid Z-Leu-Phe-COOH was the best inhibitor for calpain I (KI = 0.0085 microM) and calpain II (KI = 0.0057 microM) discovered in this study. It is likely that the inhibitors are transition-state analogs and form tetrahedral adducts with the active site cysteine of cysteine proteases and form hydrogen bonds with the active site histidine and possibly another hydrogen bond donor in the case of monosubstituted amides. Several inhibitors prevented spectrin degradation in a platelet membrane permeability assay and may be useful for the treatment of diseases which involve neurodegeneration.

Amides↗