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Model studies are presented that suggest the mechanism of the lanthanide(III) salt catalysed mono acylation of symmetrical diols proceeds via chelation of the diol and the anhydride to the lanthanide salt, followed by an 'intramolecular' acyl transfer.
Reaction of 1,3-dimesitylimidazolium chloride [IMesH]Cl with InMe3 results in (IMes)InMe2Cl, which on treatment with one equivalent of TMS-OTf affords (IMes)InMe2(OTf), which can be converted to the bistriflate complex (IMes)In(Me)(OTf)2 on addition of HOTf.
Trinuclear Ni-Cu-Ni and Ni-Ni-Ni complexes derived from an Ni(ii)-dicarboxamido-dithiolato metallosynthon exhibit redox behavior and CO binding properties similar to those of the A-cluster in acetyl coenzyme A synthase/CO dehydrogenase (ACS/CODH).
Desmosine-enriched peptides were isolated from a thermolysin digest of bovine ligamentum nuchae elastin and a partial sequence was determined. A 'two-cross-link' model is proposed in which a second cross-link, perhaps lysinonorleucine, joins two peptide chains approx. 35 amino acid residues removed from the desmosine. Implied in this model is a certain asymmetry or directionality which places restrictions on the 'sense' of the peptide chains (either always parallel or anti-parallel) in order to align the cross-linking sites. Imposing such restrictions raises the possibility of specific alignment of elastin precursor molecules by microfibrillar proteins and/or aligning peptides on the precursor molecules themselves.
1. The irradiation-inactivation procedure was used to study changes in the state of association of the protein components of adenylate cyclase in intact rat liver plasma membranes by measurement of alterations in the target size determined from the catalytic activity of the enzyme. 2. A decrease in target size at 30 degrees C in response to p[NH]ppG (guanosine 5'-[betagamma-imido]triphosphate) or GTP was demonstrated, which we take to reflect the dissociation of a regulatory subunit. The effect of GTP is potentiated by glucagon. This effect is not observed at 0 degrees C. 3. An increase in target size was observed in response to glucagon in the absence of guanine nucleotides, which we take to reflect the association of glucagon receptor with adenylate cyclase. 4. We propose a model for the activation of adenylate cyclase by glucagon in which the binding of the hormone to its receptor causes an initial association of the receptor with the catalytic unit of the enzyme and a regulatory subunit to form a ternary complex. The subsequent activation of the adenylate cyclase results from the dissociation of the ternary complex to leave a free catalytic unit in the activated state. This dissociation requires the binding of a guanine nucleotide to the regulatory subunit. 5. The effects of variation of temperature on the activation of adenylate cyclase by glucagon and guanine nucleotides were examined and are discussed in relation to the irradiation-activation data. 6. The effectiveness of hormones, guanine nucleotides and combinations of hormone and guanine nucleotides as activators of adenylate cyclase in both rat liver and rat fat-cell plasma membranes was studied and the results are discussed in relation to the model proposed, which is also considered in relation to the observations published by other workers.
An integrated microstructural and optical model for carbonaceous mesophases is developed and used to explain the principles that govern the formation and stability of experimentally observed disclination lattices. The model is able to capture the orientation features of disclination lattices, including the type and location of disclination lines, and the orientation field in the mesophase matrix. The optical model based on reflection polarized optical microscopy is able to replicate all the details observed in actual observations. The typical brush figures have the proper distribution, orientation, and intensity. The computational predictions offer science-based routes to create and control desirable material architectures based on carbonaceous mesophase-carbon fiber composites.
An atomistic model of layered double hydroxides, an important class of nanoporous materials, is presented. These materials have wide applications, ranging from adsorbents for gases and liquid ions to nanoporous membranes and catalysts. They consist of two types of metallic cations that are accommodated by a close-packed configuration of OH- and other anions in a positively charged brucitelike layer. Water and various anions are distributed in the interlayer space for charge compensation. A modified form of the consistent-valence force field, together with energy minimization and molecular dynamics simulations, is utilized for developing an atomistic model of the materials. To test the accuracy of the model, we compare the vibrational frequencies, x-ray diffraction patterns, and the basal spacing of the material, computed using the atomistic model, with our experimental data over a wide range of temperature. Good agreement is found between the computed and measured quantities.
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The chance mechanism of cell damage and of repair in the course of irradiation involves two details familiar to biologists that thus far seem to have been overlooked in mathematical treatment. One of these details is that, generally, the passage of a single "primary" radiation particle generates a "cluster" of secondaries which can produce "hits" that damage the living cell. With high linear energy transfer, each cluster contains very many secondary particles. With low linear energy transfer, the number of secondaries per cluster is generally small. The second overlooked detail of the chance mechanism is concerned with what may be called the time scales of radiation damage and of the subsequent repair. The generation of a cluster of secondary particles and the possible hits occur so rapidly that, for all practical purposes, they may be considered as occurring instantly. On the other hand, the subsequent changes in the damaged cells appear to require measurable amounts of time. The constructed stochastic model embodies these details, the clustering of secondary particles and the time scale difference. The results explain certain details of observed phenomena.
Carnitine octanoyltransferase (COT) and carnitine palmitoyltransferase (CPT) I, which facilitate the transport of medium- and long-chain fatty acids through the peroxisomal and mitochondrial membranes, are physiologically inhibited by malonyl-CoA. Using an "in silico" macromolecular docking approach, we built a model in which malonyl-CoA could be attached near the catalytic core. This disrupts the positioning of the acyl-CoA substrate in the channel in the model reported for both proteins (Morillas, M., Gómez-Puertas, P., Roca, R., Serra, D., Asins, G., Valencia, A., and Hegardt, F. G. (2001) J. Biol. Chem. 276, 45001-45008). The putative malonyl-CoA domain contained His(340), implicated together with His(131) in COT malonyl-CoA sensitivity (Morillas, M., Clotet, J., Rubi, B., Serra, D., Asins, G., Ariño, J., and Hegardt F. G. (2000) FEBS Lett. 466, 183-186). When we mutated COT His(131) the IC(50) increased, and malonyl-CoA competed with the substrate decanoyl-CoA. Mutation of COT Ala(332), present in the domain 8 amino acids away from His(340), decreased the malonyl-CoA sensitivity of COT. The homologous histidine and alanine residues of L-CPT I, His(277), His(483), and Ala(478) were also mutated, which decreased malonyl-CoA sensitivity. Natural mutation of Pro(479), which is also located in the malonyl-CoA predicted site, to Leu in a patient with human L-CPT I hereditary deficiency, modified malonyl-CoA sensitivity. We conclude that this malonyl-CoA domain is present in both COT and L-CPT I proteins and might be the site at which malonyl-CoA interacts with the substrate acyl-CoA. Other malonyl-CoA non-inhibitable members of the family, CPT II and carnitine acetyltransferase, do not contain this domain.
Research on the relationship between job-related stress and well-being has focused largely on organizational work contexts. Using a Dutch sample, we examined stress in a typical family business setting--the family farm--to explore how the farm wife's contribution to farm work is related to her well-being. We used LISREL to test an explanatory model based on the Michigan stress approach. In this model, farm women's farm contributions and their predictors, perceived role and financial stressors, husband support, self-esteem, and mental and physical health complaints were included. The results show that husband support is more important for farm women's well-being than the role-related or financial stressors. The implications of the findings are briefly discussed.
Human prorenin, secreted from a Chinese hamster ovary cell line transfected with the cDNA for preprorenin, has been purified in mg quantities by a novel single-step procedure. The method takes advantage of reversible acid activation as a means of generating active prorenin that may be bound and eluted from an affinity column for renin. Analysis of the prorenin so purified revealed that it contained about 80% intact zymogen; the remaining 20% comprised a mixture of various prorenin derivatives truncated in the prosegment, and a small amount of renin. After exposure to 37 degrees C and pH 7.5, the refolded, partially active preparation was passed once more over the affinity column to remove renin and any truncated prorenin forms that were still active and that were, therefore, again retained by the column. Over a period of several hours, refolded and inactive prorenin not bound to the column slowly regains 5% to 10% renin activity, even when maintained under conditions that are optimal for zymogen inactivation. This activity is observed toward both model peptide substrates and natural human angiotensinogen. On the basis of these findings, we propose a model in which, under physiological conditions, a small amount of open, active prorenin is in equilibrium with a predominant, closed, and inactive form of the zymogen. Support for the model is provided by binding studies with a strong renin inhibitor that displaces the equilibrium entirely to a 1:1 zymogen:inhibitor complex. Limited cleavage of prorenin by several different proteinases has provided a number of fully active renin derivatives with varying N-terminal sequences. Results thus obtained, together with analysis of prorenin and its truncated forms bound, or not bound, to the affinity column under a variety of conditions, suggest that the propeptide region, -Arg-Ile-Phe-Leu-Lys- (positions 10P-14P), is essential for the reversible refolding of the prosegment that leads to zymogen inactivation.
SUMMARY: SChiSM is a program for creating World Wide Web (WWW) pages that include embedded interactive molecular models using the browser plug-in, CHIME:, for visualization. The program works with Netscape 4.x and Internet Explorer 5 browsers to facilitate Chime/Rasmol scripting control of a molecular display.
UNLABELLED: SChiSM2 is a web server-based program for creating web pages that include interactive molecular graphics using the freely-available applet, Jmol, for illustration. The program works with Internet Explorer and Firefox on Windows, Safari and Firefox on Mac OSX and Firefox on Linux. AVAILABILITY: The program can be accessed at the following address: http://ci.vbi.vt.edu/cammer/schism2.html.
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Finite element models (FEMs) and analytical and experimental models based on poroelastic constitutive laws were developed for rhesus spinal motion segments (SMSs). Long-time creep, transient creep, and impact were studied for SMSs with normal and simulated degenerated discs. The results suggested that long-time creep observed in excised SMSs may be reduced in the in vivo SMS. The fluid phase included in these FEMs was shown to play a significant role in the mechanical response of SMSs. Relative fluid motion fields predicted in the SMS could be related to nutritional paths to the avascular interior of the disc and were found to be very sensitive to changes in discal stiffness. Reduced disc height, increased discal bulge, altered fluid motion, and stresses were quantified and may be related to mechanical failure, disc degeneration, and low-back pain.
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