Theoretical Study of the TiO2 and MgO Surface Acidity and the Adsorption of Acids and Bases

We present ab-initio periodic Hartree–Fock calculations (crystal program) of small molecules on TiO₂ and MgO. The adsorption of the molecules may be molecular or dissociative. This depends on their acid and basic properties in the gas phase. For the molecular adsorption, the molecules are adsorbed as bases on Ti(+IV) sites, the adsorption energies correlate with the proton affinities. The dissociations on the surface correlate with the gas phase cleavages: thus, the dissociation of MeOH leads to a preferential basic cleavage (the fragment HO– is adsorbed on a Ti⁺⁴ ion and the fragment Me⁺ is adsorbed on a O²– ion of the oxide). The opposite result is obtained with MeSH. Another important factor is the adsorbate–adsorbate interaction: favorable cases are a sequence of H-bonds for the hydroxyl groups resulting from the water dissociation and the mode of adsorption for the ammonium ions. Lateral interactions also force the adsorbed CO₂ molecules to bend over the surface so that their mutual orientation resembles the geometry of the CO₂ dimer. With respect to water adsorption, MgO appears to be a basic oxide. As experimentally observed, NH₃ adsorbs preferentially on TiO₂ and CO₂ on MgO. However, this difference of reactivity should not be expressed in terms of acid vs. basic behaviour but in terms of hard and soft acidity. The MgO surface is a 'soft' acidic surface that reacts preferentially with the soft base, CO₂.     

Studies on the conformations of sialyloligosaccharides and implications

Theoretical investigations, using semi-empirical potential functions have been carried out to predict the favoured conformations of the terminal dissaccharide fragments of various sialyloligosaccharides. The proposed conformational similarity for these fragments has been correlated to the binding specificity of neuraminidases. These calculations predict that bacterial neuraminidases have a binding site which can accommodate only two sugar residues and virus neuraminidases have a binding site which can accommodate more than two sugar residues.     

Inhibition of surfactant release from isolated type II cells by compound 4880

Release of [³H]phosphatidylcholine from pulmonary Type II epithelial cells was stimulated by terbutaline, forskolin and cytochalasin D. Compound $\text{48}\text{80}$ inhibited both basal and agonist-stimulated release of [³H]PC. The IC₅₀ for inhibition by compound $\text{48}\text{80}$ was 1–2 μg/ml, and was similar for inhibition of both basal and stimulated release of [³H]phosphatidylcholine. Inhibitory effects of $\text{48}\text{80}$ were noted following a 1 h exposure to compound $\text{48}\text{80}$ and persisted up to 3 h. The inhibitory effect of compound $\text{48}\text{80}$ was entirely reversed by removing compound $\text{48}\text{80}$ from the external milieu. Compound $\text{48}\text{80}$ had no effect on cytosolic cyclic AMP levels or lactate dehydrogenase release. Inhibition of surfactant release produced by compound $\text{48}\text{80}$ was unaffected by changes in extracellular calcium concentrations. Compound $\text{48}\text{80}$ is a non-toxic inhibitor of phosphatidylcholine release from Type II epithelial cells.     

Fluorescence studies using synchrotron radiation on normal and differentiated cells labeled with parinaric acids

Changes in membrane properties during the differentiation process in K562 cells have been investigated. A decrease of lectin-induced agglutination has been detected. The agglutination assay revealed to be an early and sensitive test to monitor the induced differentiation of the K562 cells. Naturally occurring fluorescent fatty acids (cis- and trans-parinaric acids) and the recently developed multifrequency phase and modulation technique were used to study cell membrane properties. Changes in fluorescence lifetime and polarization are clearly associated with cell differentiation, suggesting the involvement of the cellular plasma membrane in the differentiation process.     

Intrinsic factor secretion from isolated human gastric mucosal cells

Human gastric mucosal cells were isolated from the resected fundic mucosa of peptic ulcer patients. The intracellular content and secretion of intrinsic factor were estimated by binding to cyano[⁵⁷Co]cobalamin. The content was maximal in the enriched parietal cell fraction which also displayed the highest H⁺ production as measured by amino[¹⁴C]pyrine uptake. Secretagogues evoked full response after 15 min of incubation: pentagastrin (181% of basal secretion), carbachol (208%), histamine (250%) and dibutyryl cyclic adenosine monophosphate (304%). The phosphodiesterase inhibitor isobutylmethylxanthine was slightly more effective even than dibutyryl cAMP. The response to histamine was abolished by ranitidine, indicating activation of adenylate cyclase via histamine H₂ receptors, but remained unaffected by atropine, which in turn blocked the carbachol effect, whereas ranitidine was ineffective. The mean formation rate was 8.4 fmol intrinsic factor/10⁶ cells per h under basal conditions and 14.3 fmol in response to histamine.     

Evidence for intracellular formation of angiotensins: coexistence of renin and angiotensin-converting enzyme in Leydig cells of rat testis

Leydig cells were purified from rat testes by discontinuous metrizamide density gradient and were shown to contain renin (EC 3.4.99.1), angiotensin-converting enzyme (dipeptidyl carboxypeptidase, (EC 3.4.15.1), and the peptide hormone angiotensins I, II and III as determined by the combined HPLC and radioimmunoassay. In germinal cells only angiotensin II (AII) was found at a significant level. These findings provide evidence for intracellular formation of AII in testicular cells and demonstrate that an intracellular renin-angiotensin system exists in normal non-transformed cells.     

Brain CCK receptors are structurally distinct from pancreas CCK receptors

Brain and pancreas cholecystokinin (CCK) receptors differ markedly in their selectivity for CCK analogs. To determine the size and subunit structure of the brain CCK receptor and compare it to that of the pancreas, 125I-CCK33 was covalently cross-linked with ultraviolet light to its receptor on mouse brain particles and purified pancreatic plasma membranes. When CCK was crosslinked to brain membranes, a single consistent major labeled protein band of Mr = 55,000 was observed in both the presence and the absence of DTT. These data with brain receptors contrast to results with pancreatic receptors where two bands of Mr = 120,000 and 80,000 are labeled in the absence and presence of DTT, respectively. These studies indicate, therefore, that the brain and pancreas CCK receptors are structurally and functionally distinct.     

Selective activation of cyclic AMP dependent protein kinase by calcitonin in a calcitonin secreting lung cancer cell line

When the F1-ATPase from the thermophilic bacterium, PS3, was inactivated by 90% with 7-chloro-4-nitro[14C]benzofurazan ([14C]Nbf-Cl) at pH 7.3 and then gel-filtered, 1.25 mols of [14C]Nbf-O-Tyr and less than 0.1 mol of Nbf-N-Lys were formed per mol of enzyme. After adjusting the pH of the gel-filtered, modified enzyme to 9.0 and incubating it for 14 hrs. at 23 degrees C to promote O----N migration, 0.68 mol of Nbf-N-Lys were formed per mol of enzyme while about 16% of the original activity reappeared. Isolation of the subunits after the O----N migration showed that 90% of the incorporated 14C was present in the beta subunit, which contained 0.21 mols of [14C]Nbf-N-Lys per mol. A tryptic peptide which contained the majority of the 14C incorporated into the beta subunit was isolated and subjected to automatic amino acid sequence analysis contained 38 residues. The amino acid sequence immediately around the lysine residue labeled with [14C]Nbf-, K*, was found to be: ...I-G-L-F-G-G-A-G-V-G-K*-T-V-L-I-G... .     

Detection of protein in polyacrylamide gels using an improved silver stain

A much improved silver staining procedure for the detection of protein in polyacrylamide gels of 0.8-3.0 mm thickness is described. It achieves very high sensitivity (detecting less than 0.01 ng bovine serum albumin/mm2) by overstaining and subsequently removing nonspecific background stain using a modified, reliable destaining procedure. Maximum sensitivity follows prediamine equilibration in 0.1% (w/v) formaldehyde solution. With two-dimensional electrophoresis the improved staining procedure reveals greater than 200 polypeptides in unconcentrated human urine and greater than 150 polypeptides in a single human fingerprint.