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Bachrach U 《Current protein & peptide science》2005,6(6):559-566
The naturally occurring polyamines, spermine [NH2(CH2)3NH(CH2)4NH(CH2)3NH2] and spermidine [NH2(CH2)3NH(CH2)4NH2], as well as the diamine putrescine [NH2(CH2)4NH2], are widely spread in nature. They occur in plants, micro-organisms and animal tissues and fulfil many important physiological functions. Due to their cationic nature they interact with negatively charged macromolecules such nucleic acids, phospholipids and proteins. This ionic interaction, which is reversible, leads to the stabilization of DNA, tRNA, membranes and some proteins. Early studies demonstrated that polyamines stimulate the growth of pro- and eukaryotic cells and that they play an important role in carcinogenesis and in malignant transformation processes. As a result of these studies various inhibitors of polyamine biosynthesis have been synthesized and are used to combat cancer and parasitic diseases (e.g., African sleeping sickness). 相似文献
3.
Steven M. Bachrach 《Journal of computational chemistry》1989,10(3):392-406
A general survey of the topological properties of various phospines, phosphaalkenes, and phosphaalkynes is presented. Fifteen compounds containing carbon-phosphorus single, aromatic, double, and triple bonds were optimized at the Hartree-Fock-self-consistent field (HF-SCF) level using the 3-21G, 3-21G(*) and 6-31G* basis sets. Inclusion of d-orbitals was necessary to obtain reasonable structures. The electron densities of these compounds were analyzed using the topological method of Bader, revealing a number of trends. The value of the electron density at the P C bond critical point correlates strongly with the bond distance and bond order. Integrated electron populations correlate with coordination number. The integrated charge indicates a strongly polarized C P bond in all compounds. Comparisons with five C N compounds are made. 相似文献
4.
Bachrach SM 《SAR and QSAR in environmental research》2002,13(3-4):381-390
Internet resources for the toxicological and pharmacological communities offer considerable information, however, the data is generally not amenable to machine-driven reuse. Adoption of XML standards by these (and related) communities will revolutionize the process of sharing information, promoting collaboration and discovery. 相似文献
5.
The reaction of cyclo-l-cystine with thiolate is examined at the B3LYP/6-31+G level. The two isomers of cyclo-l-cystine differ in their dihedral angle about the disulfide bond; the M isomer (with dihedral angle of -90.1 degrees) is found to be slightly lower in energy. The nucleophilic substitution reaction at sulfur follows the addition-elimination mechanism, exemplified by the hypercoordinate sulfur intermediate on the reaction surface. The reaction is exergonic (DeltaG = -6.16 kcal mol(-1)), and both the entrance and exit transition state lie below the reactant energies. 相似文献
6.
Background
Histatins are histidine rich polypeptides produced in the parotid and submandibular gland and secreted into the saliva. Histatin-3 and ?5 are the most important polycationic histatins. They possess antimicrobial activity against fungi such as Candida albicans. Histatin-5 has a higher antifungal activity than histatin-3 while histatin-3 is mostly involved in wound healing in the oral cavity. We found that these histatins, like other polycationic peptides and proteins, such as LL-37, lysozyme and histones, interact with extracellular actin.Results
Histatin-3 and ?5 polymerize globular actin (G-actin) to filamentous actin (F-actin) and bundle F-actin filaments. Both actin polymerization and bundling by histatins is pH sensitive due to the high histidine content of histatins. In spite of the equal number of net positive charges and histidine residues in histatin-3 and ?5, less histatin-3 is needed than histatin-5 for polymerization and bundling of actin. The efficiency of actin polymerization and bundling by histatins greatly increases with decreasing pH. Histatin-3 and ?5 induced actin bundles are dissociated by 100 and 50 mM NaCl, respectively. The relatively low NaCl concentration required to dissociate histatin-induced bundles implies that the actin-histatin filaments bind to each other mainly by electrostatic forces. The binding of histatin-3 to F-actin is stronger than that of histatin-5 showing that hydrophobic forces have also some role in histatin-3- actin interaction. Histatins affect the fluorescence of probes attached to the D-loop of G-actin indicating histatin induced changes in actin structure. Transglutaminase cross-links histatins to actin. Competition and limited proteolysis experiments indicate that the main histatin cross-linking site on actin is glutamine-49 on the D-loop of actin.Conclusions
Both histatin-3 and ?5 interacts with actin, however, histatin 3 binds stronger to actin and affects actin structure at lower concentration than histatin-5 due to the extra 8 amino acid sequence at the C-terminus of histatin-3. Extracellular actin might regulate histatin activity in the oral cavity, which should be the subject of further investigation.7.
The effect of microsolvation on the deprotonation energies of uracil was examined using DFT. The structures of uracil and its N(1) and N(3) conjugate bases were optimized with zero to six associated water molecules. Multiple configurations (upward of 93) of these hydrated clusters were located at PBE1PBE/6-311+G(d,p). Trends in these geometries are discussed, with the waters generally forming chains with small numbers of waters (one-three), rings (three-five waters), or cages (five-six waters). The difference in energy between the N1 and N3 conjugate bases is 13 kcal mol(-1) in the gas phase, and it decreases with each added water up to four. At this point the energy difference has been halved, but addition of a fifth or sixth water has little effect on the energy difference. This is understood in terms of the water structures and their ability to stabilize the negatively charged atoms in the conjugate bases. 相似文献
8.
We report on new angle-resolved photoemission studies of Si(111) 2 × 1 and 7 × 7 surfaces. The emission from the 2 × 1 surface shows much structure. For normal emission the energy positions are insensitive to the photon energy in the range 19–27 eV. The emission has been interpreted as a probe of the surface density of states, SDOS, including both surface states, resonances and bulk-like states. The SDOS was also calculated as a function of parallel momentum k∥ for a model of the Si(111) 2 × 1 surface obtained from energy minimization considerations. We identify emission from the dangling bond band, which has a positive dispersion of 0.6 eV, and also emission from surface resonances which have some character of the compressed and stretched back bonds. There are also other predicted surface resonances that correspond to experimental peaks which have not been identified in previous work. Except for the dangling bond band, the surface resonances are limited in k∥ space, so that it is not possible to follow these resonance bands over all angles. Maximum intensity for the normal emission from the dangling bond is obtained at 23 eV, while the emission from the lowest s-like states monotonically increases towards 30 eV photon energy. When annealing the cleaved 2 × 1 surface to the 7 × 7 reconstructed surface, the spectra broaden significantly. The intensity of the dangling bond decreases and we see a very small metallic edge. 相似文献
9.
Polydimethylsiloxane, which is a biologically inert polymer, was used as a carrier polymer for drugs. Functional groups were introduced into the polymer to enable attachment to drugs. Polymers (and oligomers) having carboxyl, amine or hydroxyl groups were prepared from polydimethylsiloxanes having different distributions of SiH groups which were added to the C=C double bond of unsaturated acids, amines or alcohols. These polymers were reacted with suitable functional groups on drugs such as digoxin, quinidine, barbiturates, amphetamine, naloxone and atropine. 相似文献
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