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Biomedical subjects

R E Richards

Publications and source records attributed to R E Richards.

14 recordsLinked to original sources
PubMed1978

A hydrogen-deuterium exchange study of the amide protons of polymyxin B by nuclear-magnetic-resonance spectroscopy.

1. Proton magnetic resonance spectra at 270 MHz of polymyxin B, a cationic oligopeptide antibiotic, show the influence of the inorganic counteranion present in solution. 2. Hydrogen-deuterium exchange rates for the amide protons are of two types, depending on whether the anion is monovalent or polyvalent. Polyvalent anions catalyse the acid-catalysed reaction more than the monovalent anions. 3. The structure in solution was monitored using the proton signals of the amides, the phenylalanine aromatic protons, and the leucine methyl and gamma-CH protons in several polymyxin salts. The temperature coefficients of the chemical shifts of the N-H protons are used to identify two beta turns in the cyclic ring of polymyxin B. The variation in chemical shift of the N-H protons, the aromatic protons and the leucine protons are correlated with anionic size and electronegativity.

Amino Acid Sequence↗
PubMed1978

Phosphorus nuclear-magnetic-resonance studies of compartmentation in muscle.

1. Phosphorus nuclear-magnetic-resonance measurements were made on rat vastus lateralis muscle. 2. In the absence of oxygenation, the resonance from P1 broadens, as the 'energy pool' of the muscle gradually runs down. This, together with measurements of transverse relaxation times (T2) indicate that the intracellular pH is not uniform within the muscle volume. 3. Incubation of the muscle with acetate buffer at low pH (5.2) results in splitting of the P1 resonance into two components; one corresponds to phosphate in a low-pH environment and the other to phosphate in its original environment. These observations indicate that P1 is distributed among different compartments in the muscle cell. 4. Compartmentation of sugar phosphate (mainly glucose 6-phosphate) is also indicated by this method, but no evidence has been obtained for this type of compartmentation of ATP and phosphocreatine.

Acetates↗
PubMed1977

Perturbations of model protein systems as a basis for the central and peripheral mechanisms of general anaesthesia.

Protein perturbations associated with anaesthetic interactions are relevant to: (a) the central molecular mechanisms of general anaesthesia; (b) the molecular basis of physiological selectivity and anaesthetic specificity of the many 'side-effects' of anaesthesia; (c) the use of anaesthetic agents as selective hydrophobic probes for the study of protein structures and activities in detail. Small but specific protein perturbations have been studied with various nuclear magnetic resonance procedures with haemoglobin as a model protein to establish the 'ground-rules' for anaesthetic-macromolecule interactions. The correlation of one aspect of these perturbations with anaesthetic potency and hydrophobic solubility indicates that hydrophobic pockets in proteins can behave like bulk-lipid phases in terms of their solubility characteristics. Other aspects appear to depend on physical characteristics such as size, geometry, structure and composition of the individual agents. These data support the hypothesis that anaesthetic actions can be explained on a molecular basis by direct interactions with proteins in addition to lipid and aqueous effects.

Anesthesia, General↗
PubMed1976

Factors affecting the motion of the polar headgroup in phospholipid bilayers. A 31P NMR study of unsonicated phosphatidylcholine liposomes.

(1) The 129 MHZ and 36.4 MHZ 31 P NMR spectra of unsonicated liposomes consisting of phosphatidylcholines of varying chain length and unsaturation have been investigated. (2) In the liquid crystalline state the 31 P NMR liposome spectra are similar for both saturated and unsaturated phosphatidylcholines, demonstrating that the motion of the polar headgroup is not sensitive to the fatty acid composition in the disordered liquid crystalline state. (3) Below the hydrocarbon phase transition temperature there is a marked increase in the linewidth of the 31P NMR liposome spectra, indicating a reduction in the motion of the polar headgroup. (4) The addition of equimolar concentrations of cholesterol to phosphatidylcholine eliminates phase transition effects experienced by the polar headgroup. The motion of the polar headgroup is then very similar to that obtained in the liquid crystalline state for pure phosphatidylcholine bilayers. (5) In the liquid crystalline state the motion of the polar headgroup in the phosphate region is insensitive to changes in the available area per phosphatidy-choline molecule.

Binding Sites↗
PubMed1976

Conformational changes associated with transient activation of phosphorylase in glycogen particles. Studies using activity, electron-spin-resonance and phosphorus-nuclear-magnetic-resonance measurements.

1. Calcium-dependent transient phosphorylation of phorphorylase b has been monitored in a rabbit muscle glycogen particle fraction. Using a phosphorus nuclear magnetic resonance assay, the changes in concentrations of small phosphate-containing metabolites associated with this event have been measured. In addition, the conformation of phosphorylase has been monitored during transient activation by observing changes in the electron spin resonance signal from added spin-labelled phosphorylase. 2. The transient activation was associated with a loss of glucose-6-phosphate from phosphorylase b; newly formed phosphorylase a binds the nucleotides ADP, AMP, or IMP. Because of the fast interconversion of these nucleotides the species bound to phosphorylase a change throughout the process. 3. Lowering the [Mg2+] : [Ca2+] ratio during transient activation causes accumulation of ADP. Electron spin resonance data from spin-labelled phosphorylase shows that, under these conditions, ADP binding to phosphorylase a is potentiated. 4. Calcium-dependent activation in the glycogen particle fraction is compared to the activation of phosphorylase in vivo.

Animals↗
PubMed1976

Phosphorus nuclear magnetic resonance of Acholeplasma laidlawii cell membranes and derived liposomes.

1. The 129 MHz 31P-NMR spectrum of Acholeplasma laidlawii membranes is very similar to the spectrum of the derived liposomes and is a typical "solid state" spectrum in which the major contribution to the linewidth is made by the chemical shift anisotropy. From the value of the chemical shift anisotropy an order parameter of 0.15 is estimated for the lipid phosphates in both membranes. 2. The 31P-NMR spectrum of the A. laidlawii membrane is insensitive to pronase digestion of 4-60% of the membrane proteins and subsequent cytochrome C binding. These results indicate that either no strong lipid polar headgroup-protein interactions occur in the membrane or that the lipid-protein "complexes" in the membrane have a fast rotation (Tc shorter than 10(-6)S) along an axis perpendicular to the plane of the membrane. 3. Phospholipase A2 degrades all the phosphatidylglycerol in the membrane. The resulting membrane contains a phosphoglycolipid as the sole phosphorus-containing compound. The 31P-NMR spectrum of these membranes is identical to the spectrum of the native membranes suggesting a similar motion for the phosphate groups in both lipids. 4. Ca2+ binding to liposomes prepared from either the total polar lipids or the total phosphorus-containing lipids isolated from the A. laidlawii membrane does not affect the 21P-NMR spectrum. 5. The 31P-NMR spectrum of the membranes and derived liposomes, however, is sensitive to lipid phase transitions. When the membrane lipids are in the gel state a broadening of the 31P resonance occurs demonstrating that the polar head group motion in a biological membrane is more restricted below the lipid-phase transition temperature.

Acholeplasma laidlawii↗
PubMed1975

Physical studies on phosphonium phosphatidylcholine. A unique [31P]phosphorus nuclear-magnetic-resonance probe for model and biological membranes.

1. Distearoyl phosphatidylcholine and the phosphonium analogue, in which the nitrogen atom is replaced by phosphorus, show similar gel-liquid crystalline transition temperatures as detected by differential scanning calorimetry. 2. The temperature-dependence of the 31P n.m.r. (nuclear-magnetic-resonance) linewidths of the phosphate resonances of sonicated vesicles of distearoyl phosphatidylcholine and the phosphonium analogue are similar. Below the phase-transition temperature the linewidths decrease as the temperature is raised. Above the phase-transition temperature the phosphate resonances are relatively temperature-independent. The phosphonium 31P n.m.r. signal exhibits the same pattern of temperature-dependence. 3. The 31P n.m.r. phosphonium resonance is sensitive to the paramagnetic shift reagent, K3Fe(CN)6. Use of K3Fe(CN)6, together with Nd(NO3)3, enabled the determination of the trans-bilayer distribution of egg-yolk phosphatidylcholine and its phosphonium analogue in co-sonicated vesicles. Both are distributed comparably across the bilayer of the vesicles. 4. The phosphonium 31P n.m.r. signal is much sharper than the corresponding phosphate resonance in both sonicated and unsonicated dispersions of the phosphatidylcholine analogue. 5. The properties of the phosphonium analogue of phosphatidylcholine are discussed in terms of its suitability as a probe of membrane structure.

Calorimetry↗
PubMed1975

Nuclear magnetic resonance studies of anaesthetic interactions with haemoglobin.

The use of 270 MHz Fourier Transform nuclear magnetic resonance (NMR) spectrometer, combined with signal processing techniques to improve resolution, enabled proton resonances from the individual aromatic residues of haemoglobin to be distinguished. In the presence of clinical concentrations of the general anaesthetic drugs halothane and methoxyflurane, specific changes in the NMR spectrum can be distinguished which probably reflect local changes of conformation. When higher concentrations of anaesthetic are used, extensive changes in the NMR spectrum occur which are consistent with non-specific binding of the anaesthetic to the hydrophobic parts of the haemoglobin molecule.

Chemical Phenomena↗