Evidence against in vitro modulation of rat liver cholesterol 7 alpha-hydroxylase activity by phosphorylation-dephosphorylation: comparison with hydroxymethylglutaryl CoA reductase

The activity of cholesterol 7 alpha-hydroxylase in rat liver microsomes was investigated under conditions favourable for phosphorylation-dephosphorylation. The enzyme activity was similar in the presence or absence of sodium fluoride during preparation. Preincubation with ATP and magnesium did not affect the enzyme activity. Cholesterol 7 alpha-hydroxylase was inhibited by alkaline phosphatase, but this inhibition was similar also after inactivation of the phosphatase. Under similar conditions, rat hepatic hydroxymethylglutaryl CoA reductase activity was clearly modulated in agreement with phosphorylation-dephosphorylation. The absence of such a modulation of cholesterol 7 alpha-hydroxylase argues against involvement of phosphorylation-dephosphorylation in the regulation of this enzyme.     

Efficient synthesis of beta-D-mannosides and beta-D-talosides by double parallel or double serial inversion

A neighboring equatorial ester group plays a highly important role in the Lattrell-Dax (nitrite-mediated) carbohydrate epimerization reaction, inducing the formation of inversion compounds in good yields. On the basis of this effect, efficient synthetic routes to beta-D-mannosides and beta-D-talosides, from the corresponding beta-D-galactosides and beta-D-glucosides, have been designed. The present routes are based on multiple regioselective acylation via the respective stannylene intermediates, followed by inversions to the corresponding manno- and talopyranoside structures by nitrite or acetate substitution. It was found that the ester group was able to induce the inversion of its two neighboring groups in high yields following either a double parallel or a double serial inversion process. By combination of direct inversion, and neighboring- as well as remote-group participation, several beta-d-mannoside and beta-D-taloside derivatives were very conveniently obtained in good yields.     

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.     

ESI‐MS/MS of expanded porphyrins: a look into their structure and aromaticity

Electrospray mass spectrometry/mass spectrometry was used to investigate the gas‐phase properties of protonated expanded porphyrins, in order to correlate those with their structure and conformation. We have selected five expanded meso‐pentafluorophenyl porphyrins, respectively, a pair of oxidized/reduced fused pentaphyrins (22 and 24 π electrons), a pair of oxidized/reduced regular hexaphyrins (26 and 28 π electrons) and a regular doubly N‐fused hexaphyrin (28 π electrons). The gas‐phase behavior of the protonated species of oxidized and reduced expanded porphyrins is different. The oxidized species (aromatic Hückel systems) fragment more extensively, mainly by the loss of two HF molecules. The reduced species (Möbius aromatic or Möbius‐like aromatic systems) fragment less than their oxidized counterparts because of their increased flexibility. The protonated regular doubly fused hexaphyrin (non‐aromatic Hückel system) shows the least fragmentation even at higher collision energies. In general, cyclization through losses of HF molecules decreases from the aromatic Hückel systems to Möbius aromatic or Möbius‐like aromatic systems to non‐aromatic Hückel systems and is related to an increase in conformational distortion. Copyright © 2016 John Wiley & Sons, Ltd.     

Direct characterization of isoquinoline alkaloids in a crude plant extract by ion-pair liquid chromatography-electrospray ionization tandem mass spectrometry: example of Eschscholtzia californica

An ion-pair HPLC-ESI-MS-MS method has been developed for the direct and rapid characterization of isoquinoline alkaloids in a crudely purified extract of the aerial parts of Eschscholtzia californica (Papaveraceae). This plant was chosen because of its increasing use in pharmaceutical industries and because its well known alkaloid composition allows the optimization of the experimental procedure through an on-line analytical sequence. Thus, 14 isoquinoline alkaloids of different types were detected and characterized. The identities of these compounds were confirmed unambigously by their fragmentation and UV spectra obtained by LC-diode-array detection. Various experiments including tandem mass spectrometry and in-orifice collision induced dissociation were performed and prove that MS-MS is a very efficient technique to identify these compounds. An explanation for each isoquinoline alkaloid type MS-MS fragmentation pattern is proposed and indicates similar neutral and/or radical losses. The order of the fragmentation depended on the type of compound but the lost fragments were similar.     

Investigating the vortex melting phenomenon in BSCCO crystals using magneto-optical imaging technique

Using a novel differential magneto-optical imaging technique we investigate the phenomenon of vortex lattice melting in crystals of Bi₂Sr₂CaCu₂O₈ (BSCCO). The images of melting reveal complex patterns in the formation and evolution of the vortex solid-liquid interface with varying field (H)/temperature (T). We believe that the complex melting patterns are due to a random distribution of material disorder/inhomogeneities across the sample, which create fluctuations in the local melting temperature or field value. To study the fluctuations in the local melting temperature/field, we have constructed maps of the melting landscape T _m(H, r), viz., the melting temperature (T _m) at a given location (r) in the sample at a given field (H). A study of these melting landscapes reveals an unexpected feature: the melting landscape is not fixed, but changes rather dramatically with varying field and temperature along the melting line. It is concluded that the changes in both the scale and shape of the landscape result from the competing contributions of different types of quenched disorder which have opposite effects on the local melting transition.     

Energy dependence of multiplicity in proton-nucleus collisions and models of multiparticle production

This is a continuation of our earlier investigation (Gurtuet al 1974Phys. Lett. 50 B 391) on multiparticle production in proton-nucleus collisions based on an exposure of emulsion stack to 200 GeV/c beam at the NAL. It is found that the ratioR _em = 〈n _s〉/〈n _ch〉, where 〈n _ch〉 is the charged particle multiplicity in pp-collisions, increases slowly from about 1 at 10 GeV/c to 1·6 at 68 GeV/c and attains a constant value of 1·71 ± 0·04 in the region 200 to 8000 GeV/c. Furthermore,R _em = 1·71 implies an effectiveA-dependence ofR _A =A ^0.18,i.e., a very weak dependence. Predictions ofR _em on various models are discussed and compared with the emulsion data. Data seem to favour models of hadron-nucleon collisions in which production of particles takes place through adouble step mechanism,e.g., diffractive excitation, hydrodynamical and energy flux cascade as opposed to models which envisage instantaneous production.