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Biomedical subjects

R B Martin

Publications and source records attributed to R B Martin.

At least 145 records · Page 8Linked to original sources
PubMed1977

Differential effects of cholesterol and lanosterol on artificial membranes.

The effects of cholesterol, 4,4-dimethylcholesterol, and lanosterol (4,4',14alpha-trimethyl-delta8,24-cholestadiene-3beta-ol) on some properties of lecithin vesicles have been compared. Unlike cholesterol, lanosterol retards the exit of trapped glucose from phospholipid vesicles only slightly. The 13C nuclear magnetic resonance spectrum of cholesterol/lecithin vesicles shows no resonances attributable to the sterol. By contrast, several resonances attributable to quaternary carbon atoms or methyl groups are seen in the 13C nuclear magnetic resonance spectrum of lanosterol/lecithin vesicles, indicating that lanosterol is much less immobilized than cholesterol. Because the membrane behavior of 4,4-dimethylcholesterol is closely similar to that of cholesterol, it is concluded that the axial 14-alpha-methyl group is responsible for the lessened membrane immobilization of lanosterol. The results emphasize the importance of a planar sterol alpha-face for interaction with phospholipid acyl chains.

Cholesterol↗
PubMed1976

Structure in the polar head region of phospholipid bilayers: A 31P [1H] nuclear Overhauser effect study.

The structure of the head-group region of some phospholipid bilayers in vesicle form has been studied and an intermolecular association of the N-methyl protons of phosphatidylcholine (PC) with the phosphate of phosphatidylethanolamine (PE) in mixed vesicles has been identified. Observation of a 31P[1H] nuclear Overhauser effect (NOE) in the phosphorus nuclear magnetic resonances of both PC and PE in mixed vesicles demonstrates an intimate dipolar interaction between some protons and the phosphorus nuclei. Substitution of deuterium for the N-methyl protons of PC eliminated the majority of the effect and necessitated the construction of a model of the bilayer surface in which the N-methyl protons of PC could interact closely with the phosphates of neighboring PE molecules. The predominant orientation of the head group must then be parallel to the bilayer surface. The amino protons of PE do not contribute significantly to the observed NOE. A corollary of these results is that there is little if any tendency for either PC or PE in the mixed vesicles to segregate into separate domains. A decrease in NOE in sphingomyelin vesicles on going from H2O to D2O suggests that an exchangeable proton contributes to the NOE. In addition the low value of the NOE observed in D2O suggests that the head-group conformation of sphingomyelin differs from that of PC.

Binding Sites↗
PubMed1976

Transmembrane asymmetry of vesicle lipids.

The role of fatty acyl chain unsaturation in promoting asymmetry in phospholipid vesicle bilayers was investigated in mixed lipid systems with differing acyl chains and a constant phosphatidylcholine headgroup. Ratios of outside to inside components were determined by nuclear magnetic resonance spectroscopy of 13C-enriched egg phosphatidylcholine. An asymmetry or disproportionation ratio is defined and used to express quantitatively how a mixture of two lipids distributes in the outer and inner vesicle surfaces. In mixed systems with 13C-enriched egg phosphatidylcholine as one component, increasing fatty acyl unsaturation in the other component results in an increasing preference of the unsaturated chains for the outer surface.

Binding Sites↗
PubMed1976

Carbon-13 magnetic resonance spectra of nucleosides and their Pd(II) complexes.

Chemical shifts occurring in carbon-13 magnetic resonance spectroscopy are utilized to assess the site of complexation of nucleosides to enPdC12 in neutral aqueous solutions. Binding occurs at N3 in cytidine, thymidine, and uridien, at N7 in 1-methylguanosine, and at N1 in guanosine. For most carbon atoms adjacent to N3 in the pyrimidine nucleosides the complexation shifts of the basic ligand are about 30% of the corresponding upfield protonation shifts. All complexes are of the form enPdL2 indicating that the ligands are unidentate and that the tendency to chelation is weak. Carbon-13 magnetic resonance spectroscopy appears to be the best method for delineating these complexes in solution. Due to the high avidity of chloride ion for Pt(II), cis dichloro Pd(II) complexes may be better models for intracellular action of the corresponding Pt(II) complexes than the Pt(II) complexes themselves.

Binding Sites↗
PubMed1976

Turf-toe: a shoe-surface related football injury.

Plantar capsule-ligament sprain of the great toe metatarsophalangeal joint, herein referred to as "turf-toe," is discussed with emphasis on two apparantly predisposing factors, playing surface hardness and shoe stiffness. Surface hardness studies have previously been performed by the authors on natural grass and AstroTurf. A study of football shoe flexibility is presented and the results correlated with the occurrence of turftoe. We have not encountered this entity in players wearing relatively stiff conventional seven posted football shoes or the more flexible soccer style shoe on natural grass fields. We have found it to be a not uncommon injury among players wearning the soccer style shoe on AstroTurf.

Athletic Injuries↗
PubMed1975

Fe(III) and Cu(II) conalbumin visible circular dichroism spectra.

The single polypeptide chain of conalbumin strongly binds two Fe(III) or two Cu(II) ions to yield intense absorption in the visible region similar to that shown by the related protein transferrin. Comparison of the metal-ion-binding sites in the two proteins is made by exploiting the sensitivity to ligand geometry of circular dichroism (CD). For the Fe(III) proteins strong similarities of the CD spectra outweigh marginal differences. For Cu(II) conalbumin an additional negative extremum near 506 nm appears between two positive ones at 634 and 410 nm suggesting greater subtraction of oppositely signed CD components leading to lesser magnitudes for the two positive peaks than are found in Cu(II)-transferrin. The two Fe(III)-binding sites within conalbumin are compared by noting the strong similarities of the CD and MCD of proteins with Fe(III) in one site and Ga(III) in the other site, and vice versa, with the protein containing Fe(III) in both sites. Due to features of the amino acid sequences of the single protein chains, the four strong metal ion binding sites in conalbumin and transferrin cannot be identical in all particulars, yet CD spectra of their metal ion complexes are closely similar. From a study of model phenolate complexes and the wavelength maxima of visible absorption in the Fe(III), Cu(II), and Co(III) proteins near 465, 440, and 405 nm, respectively, these strong absorption bands are identified as ligand to metal ion electron-transfer transitions. It is suggested that tyrosyl residues are the donors in the electron transfer transitions and that they lock in the metal ions after being keyed into position by binding of bicarbonate or other anions.

Animals↗
PubMed1975

Headgroup conformation and lipid--cholesterol association in phosphatidylcholine vesicles: a 31P(1H) nuclear Overhauser effect study.

The nuclear Overhauser effect has been observed in the nuclear magnetic resonance spectra of 31P. The information content of the nuclear Overhauser effect has been applied to the structure and dynamic properties of phosphatidylcholine vesicles. In the vesicles only 1/3 of the theoretical maximum nuclear Overhauser effect enhancement is observed. This result is accounted for by dipolar interactions between the N-methyl protons and the phosphate of phosphatidylcholine, and a correlation time for internal motion of 1.4 X 10(-9) sec. Addition of up to 30% cholesterol does not change the nuclear Overhauser effect enhancement or spin-lattice relaxation time of the vesicles. It is argued that the OH group of cholesterol is hydrogen bonded to the ester carbonyl oxygen of the phosphatidylcholine molecules.

Cholesterol↗
PubMed1975

Cleat-surface friction on new and old AstroTurf.

The authors have studied the alterations in cleat-surface friction of AstroTurf associated with use and exposure. Three cleat types were studied on five year old turf and on an unused, unexposed turf sample of the same production batch. Tests were carried out with and against surface grain under wet and dry conditions. It was found that with use and exposure the surface friction of AstroTurf does change, affecting both player performance and safety.

Athletic Injuries↗
PubMed1974

Pyrrole hydrogen ionization of imidazole derivatives in metal ion complexes and carbonic anhydrase.

Zinc ion-induced pyrrole hydrogen ionization from a histidyl residue has recently been suggested as the source of the activity-related deprotonation in carbonic anhydrase (EC 4.2.1.1; carbonate hydro-lyase) occurring at pH 7-8. The results offered to support the hypothesis are shown to be deficient. Examination of the literature reveals no precedent for such a pronounced acidification from pK(a) [unk] 14.2 in imidazole compounds by zinc ion. It is suggested that Zn(II)-induced pyrrole ionizations in imidazoles occur with pK(a) about 13.

Carbonic Anhydrases↗
PubMed1974

Differential interaction of cholesterol with phosphatidylcholine on the inner and outer surfaces of lipid bilayer vesicles.

The separate identification of the -N(+)-(CH(3))(3) groups located on the outside and inside of phospholipid bilayers observed in proton magnetic resonance spectroscopy upon addition of low concentrations of praseodymium ion was exploited to investigate the effects of incorporated cholesterol. Only about 7% of the phosphate groups on the outside of the bilayer belong to a class of strong binding or shifting sites. Upon addition of up to about 30% cholesterol to egg lecithin bilayers, no changes in chemical shift or ratio of areas of peaks due to outer and inner -N(+)(CH(3))(3) groups appear. At about 30% incorporated cholesterol, an abrupt decrease occurs in the chemical-shift difference between -N(+)(CH(3))(3) groups located on the outer and inner bilayer surfaces, and an abrupt increase occurs in the ratio of the areas of the two peaks. For L-alpha-dipalmitoyl lecithin bilayers, an abrupt change in chemical-shift difference occurring between 10 and 20% cholesterol is not accompanied by a change in the relative number of -N(+)(CH(3))(3) groups located on the outer and inner surfaces. These results are interpreted as due to the homogeneous distribution of up to 30% cholesterol in egg lecithin bilayers. Above 30%, cholesterol is asymmetrically distributed in favor of the inner layer. In egg lecithin with a variety of polyunsaturated side chains, the side chains with the greater number of double bonds are preferentially displaced by high concentrations of cholesterol, which accounts for the increase in the ratio of outer to inner -N(+)(CH(3))(3) groups. Such preferential displacement by cholesterol cannot occur with the saturated L-alpha-dipalmitoyl lecithin. It is suggested that modified phospholipid vesicles of low radii of curvature may provide high concentrations of "active sites" present in membranes.

Binding Sites↗