Regulation of an 8-kDa peptide involved in testosterone production by luteinizing hormone in rat Leydig cells

Results of Western blot analysis carried out with an interstitial cell extract from male guinea pig and ovarian extract from immature female rats administered equine chorionic gonadotropin (eCG) provide supportive evidence to our earlier suggestion that an 8-kDa peptide is involved in acquisition of steroidogenic capacity by the rat Leydig cells. It was found that though the signal was observed in other tissues such as liver, kidney and lung which do not produce gonadal hormones, the peptide was modulated only by lutenizing hormone (LH) in the rat Leydig cells.

Effect of peptide-based captopril analogues on angiotensin converting enzyme activity and peroxynitrite-mediated tyrosine nitration

Angiotensin converting enzyme (ACE) regulates the blood pressure by converting angiotensin I to angiotensin II and bradykinin to bradykinin 1-7. These two reactions elevate the blood pressure as angiotensin II and bradykinin are vasoconstrictory and vasodilatory hormones, respectively. Therefore, inhibition of ACE is an important strategy for the treatment of hypertension. The natural substrates of ACE, i.e., angiotensin II and bradykinin, contain a Pro-Phe motif near the site of hydrolysis. Therefore, there may be a Pro-Phe binding pocket at the active site of ACE, which may facilitate the substrate binding. In view of this, we have synthesized a series of thiol-and selenol-containing dipeptides and captopril analogues and studied their ACE inhibition activities. This study reveals that both the selenol or thiol moiety and proline residues are essential for ACE inhibition. Although the introduction of a Phe residue to captopril and its selenium analogue considerably reduces the inhibitory effect, there appears to be a Phe binding pocket at the active site of ACE.

On the importance of backbone loop and peptide flip in the Walker sequence in F-1-ATPase action

The Walker sequence, GXXXXGKT, present in all the six subunits of F-1-ATPase exists in a folded form, known as phosphate-binding loop (P-loop). Analysis of the Ramachandran angles showed only small RMS deviation between the nucleotide-bound and nucleotide-free forms. This indicated a good overlap of the backbone loops. The catalytic beta-subunits (chains D, E and F) showed significant changes in the Ramachandran angles and the side chain torsion angles, but not the structural alpha-subunits (chains A, B and C). Most striking among these are the changes associated with Val160 and Gly161 corresponding to a flip in the peptide unit between them when a nucleotide is bound (chains D or F compared to nucleotide-free chain E). The conformational analysis further revealed a hitherto unnoticed hydrogen bond between amide-N of the flipped Gly161 and terminal phosphate-O of the nucleotide. This assigns a role for this conserved amino acid, otherwise ignored, of making an unusual direct interaction between the peptide backbone of the enzyme protein and the incoming nucleotide substrate. Significance of this interaction is enhanced, as it is limited only to the catalytic subunits, and also likely to involve a mechanical rotation of bonds of the peptide unit. Hopefully this is part of the overall events that link the chemical hydrolysis of ATP with the mechanical rotation of this molecule, now famous as tiny molecular motor.

Solid propellant binders

Solid, propellants are widely used in modern rockets and missiles. Although the history of solid rockets could be traced to the discovery of gunpowder over a thousand years ago, the technology could be perfected only by the later half of the 20(th) century. The failure of gunpowder rockets was largely due to the unknown consolidating technique of the powder composition. The emergence of large solid propellant motors had, to await the dawn of polymer. science and technology(S&T). Specific syntheses of functionally terminated polymers having cross-linking capability led to the emergence of casting technology of solid composite propellants. This review describes the various polymeric fuel/binder systems used or considered for use in solid,propellants. It includes a brief background, advantages, and shortcomings of the various systems, an account of the currently used binders and a critical survey of the advanced polymers envisaged for future usage. Special emphasis has been laid on recently synthesized polymers having N-N bonds in their structures, and-on the feasibility of developing smokeless propellants based on ammonium nitrate.

Synthesis and applications of propargyl pentafluorophenyl carbonate for peptide synthesis

Propargyl pentafluorophenyl carbonate was synthesised in quantitative yield by the reaction of propargyl chloroformate and pentafluorophenol. All the N-propargyloxycarbonyl (N-Poc) amino acids were obtained in good yield. The use of Poc-OPfp in peptide synthesis has been explored. (C) 2002 Elsevier Science Ltd. All rights reserved.

Entrapment of a Water Wire in a Hydrophobic Peptide Channel with an Aromatic Lining

A one-dimensional water wire has been characterized by X-ray diffraction in single crystals of the tripeptide Ac-Phe-Pro-Trp-OMe. Crystals in the hexagonal space group P6(5) reveal a central hydrophobic channel lined by aromatic residues which entraps an approximately linear array of hydrogen bonded water molecules. The absence of any significant van der Waals contact with the channel walls suggests that the dominant interaction between the ``water wire'' and ``peptide nanotube'' is electrostatic in origin. An energy difference of 16 KJmol(-1) is estimated for the distinct orientations of the water wire dipole with respect to the macrodipole of the peptide nanotube. The structural model suggests that Grotthuss type proton conduction may, through constricted hydrophobic channels, be facilitated by concerted, rotational reorientation of water molecules.

New Energetic Epoxy Binders

A new class of epoxy resins having N-N bonds in the backbone has been synthesized with a view to explore their properties as energetic binders. The N-epoxidation of bis-dicarbonylhydrazones of adipic, azelaic and sebacic dihydrazides results in the formation of viscous resins having epoxide end groups. The resins have been characterized by the elemental and end group analyses, IR and NMR spectra. Relevant properties for their use as binders in solid propellants, such as thermal stability, heat of combustion, burn rate and performance parameters of AP-based propellant systems, have been evaluated. A significant increase in the burn rate of AP-based propellants noticed, is perhaps related to the exothermicity of the binder decomposition and the reactivity of N-N bonds with perchloric acid formed during the combustion of AP.

Effect of ester chemical structure and peptide bond conformation in fragmentation pathways of differently metal cationized cyclodepsipeptides

Fragmentation behavior of two classes of cyclodepsipeptides, isariins and isaridins, obtained from the fungus Isaria, was investigated in the presence of different metal ions using multistage tandem mass spectrometry (MS(n)) with collision induced dissociation (CID) and validated by NMR spectroscopy. During MS(n) process, both protonated and metal-cationized isariins generated product ions belonging to the identical `b-ion' series, exhibiting initial backbone cleavage explicitly at the beta-ester bond. Fragmentation behavior for the protonated and metal-cationized acyclic methyl ester derivative of isariins was very similar. On the contrary, isaridins during fragmentation produced ions belonging to the `b' or/and the `y' ion series depending on the nature of interacting metal ions, due to initial backbone cleavages at the beta-ester linkage or/and at a specific amide linkage. Interestingly, independent of the nature of the interacting metal ions, the product ions formed from the acyclic methyl ester derivative of isaridins belonged only to the `y-type'. Complementary NMR data showed that, while all metal ions were located around the beta-ester group of isariins, the metal ion interacting sites varied across the backbone for isaridins. Combined MS and NMR data suggest that the different behavior in sequence specific charge-driven fragmentation of isariins and isaridins is predetermined because of the constituent beta-hydroxy acid residue in isariins and the cis peptide bond in isaridins.

Role of Nonplanar Peptide Unit in Regular Polypeptide Helices - New Model for Pply-Beta-Benzyl-L-Aspartate

The effect of non-planarity of the peptide unit on helical structures stabilized by intrachain hydrogen bonds is discussed. While the present calculations generally agree with those already reported in the literature for right-handed helical structures, it is found that the most stable left-handed structure is a novel helix, called the delta-helix. Its helical parameters are close to these reported for poly-beta-benzyl-L -aspartate. Conformational energy calculations show that poly-beta-benzyl-L -aspartate with the delta-helical structure is considerably more stable than the structure it is generally believed to take up (the omega-helix) by about 15 kcal/mol-residue.