bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative study of self‐absorption in near‐infrared Fourier transform Raman spectroscopy
Authors: Everall N.
Published: May 2005

Self‐absorption occurs in near‐infrared Fourier transform (NIR‐FT) Raman spectroscopy when the absolute frequency of a Raman band coincides with an NIR absorption band of the scattering material. This is manifested by selective attention of specific Raman bands, the degree of which depends on the sample pathlength, concentration and position in the laser beam. These factors can introduce serious errors in quantitative FT Raman applications unless care is taken. This paper describes a simple analysis which allows quantitative predictions of the effects of varying sample concentration and collection optics geometry. The predictions for concentration variation have been validated by experiment. A consideration of the experimental design required to minimize self‐absorption indicates that this will also reduce instrument sensitivity and ease of alignment; therefore, there is a trade‐off between optimizing instruments for quantitative applications whilst maintaining sensitivity and ease of use.
Low wavenumber Raman scattering in viscous liquids
Authors: Zwick A. , Landa G.
Published: May 2005

Low‐wavenumber depolarized Raman spectra (−400 to 400 cm−1) for dioxane, water and glycerol are presented. Stokes and anti‐Stokes spectra (−400 to 400 cm−1), are used to define a reduced spectrum, in which the effects of temperature and also flat backgrounds and symmetric central components are removed, without knowledge of these parameters. Comparison with the usual reductions shows that (i) all inelastically scattered photons must be considered as ‘true’ Raman signals, due to processes involving Boson‐like excitations, (ii) if central scattering exists, then its intensity also depends on the population factor, (iii) the low‐wavenumber Stokes signal is more intense than expected for a factor of n + 1 only, owing to non‐linear effects, and (iv) the systematic use of reduced spectra is not essential, and can be hazardous in some cases.
Lattice dynamic analysis of Raman data from tin tetrabromide: Chains at high pressures
Authors: Ghrist R. W. , Lee S. A.
Published: May 2005

A lattice dynamic model of chains of SnBr4 molecules is developed to analyze previously published Raman data at high pressures. This model is used to evaluate both the intra‐ and intermolecular bonding in SnBr4 up to about 10 GPa. The effective force constant associated with the intramolecular SnBr bond is found to increase in an approximately linear manner with pressure. The effective force constant of the intramolecular BrBr bond shows a dramatic decrease of about 30% near 6 GPA, the pressure at which chains of molecules begin to form in SnBr4. The effective force constant associated with the intermolecular BrBr bond rises linearly with pressure after the chains begin to form.
Resonance Raman and time‐resolved resonance Raman studies of ruthenium(II) complexes of 2,2′‐bipyridine and 5‐monomethyl‐2,2′‐bipyridine. Evidence for polarization of the 3MLCT state electron density in the asymmetric ligand
Authors: Treflert‐Ziemelis Shelly M. , Kincaid James R.
Published: May 2005

The resonance Raman and time‐resolved resonance Raman (TR3) spectra of ruthenium(II) complexes containing the asymmetric (RR)(5‐methyl‐2,2′‐bipyridine) ligand, Ru(5‐mmb), and its methyl‐deuterated analogue, Ru(5‐d3‐mmb), are reported. The spectra are compared to those of tris(2, 2′‐bipyridine)ruthenium(II), Ru(bpy), and tris(5,5′‐dimethyl‐2,2′‐bipyridine)ruthenium(II), Ru(5,5′‐dmb), and its deuterated analogue, Ru(5,5′‐d6‐dmb). The ground‐state spectrum for the asymmetric chelate is interpretable in terms of vibrationally isolated fragments with the exception of the modes involving the inter‐ring and adjacent bonds. In addition, the TR1 spectra are shown to be consistent with slight polarization of the (triplet) metal‐to‐ligand charge‐transfer, 3MLCT, excited‐state charge distribution toward the pyridinc fragment of the chelated anion.
Synthesis and polarized Raman studies of rhombohedral LuOCl single crystals
Authors: Burns J. B. , Stump N. A. , Peterson J. R.
Published: May 2005

The polarized Raman spectra of SmSI‐type rhombohedral LuOCl were recorded at various polarization orientations. The polarized spectra were analyzed to determine the symmetry assignments of the Raman‐active transitions. The Raman spectra of polycrystalline and single‐crystal LuOCl are characterized by five features. Analysis of the intensity enhancements of the three lattice vibrations at 139, 272 and 496 cm−1 indicate an Eg symmetry, whereas those at 86, 139 and 473 cm−1 exhibit intensity enhancements which indicate an A1g symmetry.
The Raman spectrum of brookite, TiO2 (Pbca, Z = 8)
Authors: Tompsett G. A. , Bowmaker G. A. , Cooney R. P. , Metson J. B. , Rodgers K. A. , Seakins J. M.
Published: May 2005

The Raman microprobe spectra of natural brookite crystals from Switzerland and Brazil and a synthetic brookite powder exhibit a characteristic intense band at 153 cm−1. In contrast, anatase has a band of similar intensity at 144 cm−1 and rutile lacks a strong band in this region. Polarization experiments with the Brazilian crystal permit 17 out of a predicted 36 vibrational bands to be readily assigned as A1g (127, 154, 194, 247, 412, 640 cm−1), B1g (133, 159, 215, 320, 415, 502 cm−1), B2g (366, 395, 463, 584 cm−1) and B3g (452 cm−1). Eight weaker bands and component sub‐bands resolved at 172, 287, 545, 618 cm−1, 254, 329, 476 cm−1 and 497 cm−1 are tentatively assigned to B3g, B2g and A1g modes respectively. Traces of Si and Fe in the Brazilian crystal and Si, Fe, Al and S in the Swiss sample are indicated by spot electron microprobe analysis. Electron spin resonance spectra suggest small amounts of Fe3+ are substituting for Ti4+ in the structure. Concomitant protonation of oxygens to maintain charge balance yields OH groups which give rise to three sharp, low‐intensity absorption bands near 3360, 3380 and 3404 cm−1 in the infrared spectra. X‐ray photoelectron spectroscopy shows that surface‐bound OH/H2O species exist in both crystals but no detectable Ti3+.
Vibrational study of diglycolic acid and potassium diglycolate salts
Authors: Ramsis H. , Perez‐Ruiz E. , Roger J. , Bourret E. , Delarbre J. L. , Maury L.
Published: May 2005

The Raman and infrared spectra of diglycolic acid and its potassium salts in aqueous solution were recorded from 4000 to 200 cm−1. Vibrational assignments were made for all the observed wavenumbers on the basis of isotopic wavenumber shift, depolarization ratios and group wavenumber considerations and comparison with accepted assignments for certain vibrational modes in other similar compounds. The three compounds (the acid, the acid salt and the neutral salt) belong to the Cs symmetry group, but their conformations are quite different. In the crystalline state, the acid salt has a strong hydrogen bond and appeared to be of type A according to Speakmann's classification.
Polarization‐sensitive resonance CSRS of deoxy‐and oxyhaemoglobin
Authors: Voroshilov Artemy , Lucassen Gerald W. , Otto Cees , Greve Jan
Published: May 2005

Polarization‐sensitive coherent Stokes Raman scattering (CSRS) measurements of oxy‐ and deoxyhaemoglobin in aqueous solutions are reported. The excitation wavelengths used were chosen in the region of the Q absorption bands to achieve twofold electronic resonance. The dispersion profiles of all independent susceptibility χ(3) components and purely anisotropic and anti‐symmetric scattering contributions were resolved within the frequency non‐degenerate CSRS scheme. Eight bands of oxyhaemoglobin and five bands of deoxyhaemoglobin were observed in the range 1500‐1680 cm−1. Simultaneously fitting sets of polarization spectra provided vibrational parameters (positions, bandwidths, amplitudes, phases and CSRS depolarization ratios) for each compound. Major bands were assigned to the non‐totally symmetric v10, v11 and v19 modes of the porphyrin macrocycle. The phases calculated exhibited a correlation with the symmetry of the vibrations. On the basis of the spectral fits, the three additional peaks arising in the oxyhaemoglobin spectra could be ascribed to the bands of intermediate deoxyhaemoglobin. The occurrence is due to the partial photolysis of oxyhaemoglobin. Vibrational parameters of these bands were found to be essentially similar to the parameters of the bands observed in the spectra of the stable deoxyhaemoglobin. Despite the asymmetric character predicted, the major bands were all contributed to by a considerable isotropic component. A decrease in the depolarization ratio P of the anomalously polarized v19 mode from 7.7 in oxyhaemoglobin to 4.3 in deoxyhaemoglobin was observed. Such a decrease in anti‐symmetric character of the vibration on release of the ligand supports the occurrence of deformation of the haem ring system.
High‐pressure Raman study of SrMoO4 up to 37 GPa and pressure‐induced phase transitions
Authors: Jayaraman A. , Wang S. Y. , Shieh S. R. , Sharma S. K. , Ming L. C.
Published: May 2005

Pressure‐induced phase changes in SrMoO4 were investigated by high‐pressure Raman spectroscopy in a diamond anvil cell. The scheelite‐type SrMoO4 transforms in to a monoclinic lattice near 13 GPa and retains this structure up to 37 GPa, the limit of pressure tested. There is no pressure‐induced amorphization in this simple molybdate up to this pressure, as in the case of structurally complex molybdate systems. The optical absorption characteristics of SrMoO4 change considerably with pressure, the sample turning progressively deep orange‐brown with increase in pressure. This change is connected with the lowering of the d‐state of molybdenum in the MoO4 ion with increase in pressure.
Dual circular polarization Raman optical activity of related terpene molecules: Comparison of backscattering DCPI and right‐angle ICP spectra
Authors: Yu Gu‐Sheng , Freedman Teresa B. , Nafie Laurence A.
Published: May 2005

The backscattering in‐phase dual circular polarization (DCPI) Raman and Raman optical activity (ROA) for a series of terpene molecules is reported. The selected molecules were studied in three groups of closely related structures and correlations between ROA features and structural elements among molecules within these groups are discussed. One aim of this study was to uncover additional details regarding the sensitivity of ROA to stereostructural features in molecules and to elucidate further the degree of local character of this new stereochemical probe. Another was to compare the backscattering DCPI ROA intensities reported here with those obtained using depolarized right‐angle incident circularly polarized (ICP) ROA for some of the same molecules more than a decade ago.
UV‐excited continuum resonance Raman scattering from 35Cl2
Authors: Vogt P. , Schmitt M. , Kiefer W.
Published: May 2005

High‐resolution Raman spectra of isotopically pure 35Cl2 were recorded using UV argon ion laser radiation of 275.4, 300.3, 302.4 and 305.5 nm. Overtone progressions could be observed for excitation with 300.3, 302.4 and 305.5 nm radiation. All overtone transitions could be simulated satisfactorily using both the traditional Kramers‐Heisenberg‐Dirac equation and time‐dependent quantum theory. The results obtained for 35Cl2 are compared to those derived earlier for I2 and Br2. The spectral features of the fundamental band for excitation in the UV region can be explained by assuming a destructive interference effect between resonant and non‐resonant Raman scattering resulting from adjacent high‐energy electronic states.
Fourier transform Raman spectroscopic study of fungi
Authors: Edwards H. G. M. , Russell N. C. , Weinstein R. , Wynn‐Williams D. D.
Published: May 2005

Fourier transform (FT) Raman spectra of the cell walls of three species of fungi are reported for the first time, namely (i) Agaricus bisporus, a fruiting bud, (ii) Mortierella genus and (iii) Mucor genus. Some molecular assignments are proposed for the major vibrational features and attributed to chitin, N‐acetylglucosamine and (R)‐glucan. Preliminary studies indicate that it is possible to use FT‐Raman spectroscopy to discriminate between different mixed species in culture media.
Low‐temperature polarized single‐crystal Raman spectra of the β‐alums CSM(SO4)2. 12H2O (M = Mo or Ru) between 275 and 1200 cm−1
Authors: Armstrong Robert S. , Beattie James K. , Best Stephen P. , Cole Bradley D. , Tregenna‐Piggott Philip L. W.
Published: May 2005

Low‐temperature, polarized, single‐crystal Raman spectra of the β‐alums CsM(SO4)2. 12H2O (M = Mo or Ru) and their deuterated analogues were recorded between 275 and 1200 cm−1. The internal modes of sulphate and [M(OH2)6]3+and the external modes of water coordinated to the mono‐ and tervalent cation were assigned. This allowed a comparison between the wavenumbers of the internal modes of second‐ and first‐row transition metal hexaaquacations. The relationship betweenv1(MO6) and the MIII—O bond length is similar for the first‐row transition and Group 13 metals, but is significantly different for the second‐row transition metals. This suggests a non‐ionic contribution to the metal‐water bonding in the latter case. The relative intensities of thev1(MO6) modes are highly dependent on the identity of the metal; however, the trend in this property is not simply related to either the bond strength, the polarizing power of the cation or the covalent interaction.
Small‐angle X‐ray scattering of human serum high‐density lipoproteins
Authors: Shipley G. G. , Atkinson D. , Scanu A. M.
Published: May 2005

Small‐angle x‐ray scattering (SAXRS) studies of the human serum high‐density lipoprotein HDL2 indicate a symmetrical particle with a radius of gyration Rg = 46 Å. The positions and intensities of subsidiary maxima in the scattering curves are not consistent with those of a uniformly electron dense sphere. Scattering curves calculated for spheres with a step‐model radial electron density distribution, show good agreement with the experimental scattering curve for HDL2 only for specific values of the step function used. The dimensions obtained for the electron‐deficient core and electron‐rich shell model are quantitatively consistent with a predominantly surface location for the HDL2 protein and phospholipid head groups, the more hydrocarbon species being located in the interior of the particle.
Lipid–protein and lipid–lipid interactions in cytochrome oxidase model membranes
Authors: Jost Patricia C. , Capadil Roderick A. , Vanderkooi Garret , Griffith O. Hayes
Published: May 2005

Two lipid environments are detected in membranous cytochrome oxidase, using spin labeling techniques. This model membrane system consists of closed vesicular membranes formed spontaneously when the membrane protein is isolated with its accompanying phospholipids. The data show both an immobilized component, which is constant in amount, and a fluid component. Based on spectral analysis, the interpretation is that the bound component represents a single layer of lipid immobilized on the surface of the protein between the hydrophobic protein complex and the adjacent fluid bilayer regions. Maximal enzyme activity of this functional protein complex is attained when all of the bound sites are occupied, and above this level additional phospholipid (bilayer) has little or no effect on the enzyme activity.
Lateral phase separations in membranes
Authors: Shimshick E. J. , Kleemann W. , Hubbell W. L. , McConnell H. M.
Published: May 2005

Lateral phase separations of phospholipids in both bacterial membranes and model membrane systems (phospholipid bilayers) can be studied using spin labels. Temperature–composition phase diagrams have been determined for binary mixtures of lipids dispersed in excess water by measurements of changes in the fluidity of the membranes as a function of temperature. These results have been used to interpret similar fluidity changes in bacterial membranes. There is evidence that the coexistence of fluid and solid lipid domains facilitates transport through membranes.
Dynamic properties and membrane activity of ion specific antibiotics
Authors: Grell E. , Funck Th.
Published: May 2005

Conformational rearrangements of membrane‐active peptide and depsipeptide antibiotics such as enniatin B, valinomycin, and valine‐gramicidin A have been studied as a function of solvent polarity employing ultrasonic absorption methods. The results provide information about the number of occupied conformational states and their respective rates of interconversion. The interpretation of the results from kinetic measurements was confirmed by spectroscopic studies.

The remarkable differences in the stabilities of the various cation complexes of depsipeptide antibiotics bound to lecithin vesicles as well as in homogeneous solution were related to different conformations of the ligands in these complexes as characterized by spectroscopic techniques. Kinetic studies by relaxation methods led to the elucidation of the mechanism of complex formation. Complexation of cations follows a multistep reaction. For valinomycin the rate‐limiting step of cation complexation is a ligand conformational change which occurs during the stepwise substitution of solvent molecules from the cation.
Bacterial mutants which block phage assembly
Authors: Georgopoulos Costa P. , Eisen Harvey
Published: May 2005

groE bacterial mutants of E. coli have been isolated on the basis of their inability to propagate bacteriophage λ. The block exerted on λ growth has been shown to operate at the level of head assembly. Some groE mutations express pleiotropic effects, such as inability to propagate T4 and T5 or inability to form colonies at high temperature. P1 transduction experiments show that these groE mutations map at 83 min on the genetic map of E. coli and that a single mutation is responsible for the pleiotropic effects observed. At 43°C, some of the groE strains are temperature sensitive for growth and form long filamentous structures. Examination of the proteins synthesized at 43° by one of the temperature‐sensitive groE strains, groEA44, by SDS gel electrophoresis reveals a pattern of synthesis somewhat different from that exhibited by the gro+ parent strain: some new bands appear, while others disappear.
Assembly of microtubules from preformed, ring‐shaped protofilaments and 6‐s tubulin
Authors: Erickson Harold P.
Published: May 2005

Tubulin obtained from disassembly of microtubules at 0°C exists in two forms: 6‐S tubulin and a larger, curved or ring‐shaped filament. These two forms have been separated chromat ographically and their roles in assembly examined. The purified rings reassemble to microtubules with high efficiency by uncoiling and straightening out, to be incorporated directly as protofilaments in the microtubule wall, and are thus identified as preformed protofilaments. Purified 6‐S tubulin has not been observed to reassemble into microtubules by itself but will contribute to assembly when mixed with rings. Addition of glycerol at 0°C induces the 6‐S tubulin to form rings, and the treated fraction will then reassemble to microtubules. Electron microscope observations indicate that assembly begins with the formation and growth of an incomplete microtubule wall. This wall grows wider by the addition of new protofilaments until the intact, circular microtubule, with 13 protofilaments, is formed. It is suggested here that growth of this wall from individual 6‐S tubulin subunits may be energetically unfavorable. The direct incorporation of preformed protofilaments may be much more favorable, in which case the rings would be required for this initial stage of assembly.
Regulation of size and birefringence of the in vivo mitotic apparatus
Authors: Rebhun Lionel I. , Mellon Margaret , Jemiolo David , Nath Jayasree , Ivy Nettie
Published: May 2005

Long chain glycols augment in size and birefringence the in vivo mitotic apparatus (MA) of marine eggs. Dinitrophenol and caffeine antagonize the effect but they can be balanced by glycols. Caffeine inhibits the phosphodiesterase for cyclic AMP (CAMP) and CAMP levels increase in its presence. However, added dibutyryl CAMP does not affect MAs or cleavage, but is taken up by eggs. Oxygen uptake studies show that caffeine depresses oxidative metabolism but does not affect ATP levels. Action through the pentosephosphate shunt is suggested.

Glycols influence the assembly of tubulin. Optical ultracentrifuge patterns of tubulin polymerized without glycol show a 6S and 30S peak. Similar patterns of tubulin polymerized at pH 6.4 in glycol and depolymerized in its absence show 6S, 8–18S, and 30S, peaks. The 8–18S peak appears in equilibrium with the 6S peak. If glycol is added to cold tubulin polymerized without glycol, only 6S and 30S peaks occur. Preparations with no 30S peak do not show 450 Å rings in the EM. Calcium depolymerizes microtubules. In the absence of glycols 450 Å rings are seen. In the presence of glycol, much higher concentrations of calcium are necessary for depolymerization, and few 450 Å rings occur.

We suggest that glycols prevent formation of the stable 30S peak, favor an intermediate structure in equilibrium with the 6S peak, and antagonize calcium depolymerization. Their in vivo effects may arise from these interactions.
Lipid phase separations and protein distribution in membranes
Authors: Kleemann W. , Grant C. W. M. , McConnell H. M.
Published: May 2005

Lateral phase separations in lipid and lipid‐protein systems are discussed with the aid of phase diagrams derived from spin‐label measurements. Freeze‐fracture data from E. coli membranes and model lipid–protein bilayers indicate that the protein tends to associate with fluid lipid phases.
Interaction of enzymes with mixed micelles of phospholipid and detergent: Analysis of the phospholipase A2–dipalmitoyl phosphatidylcholine–triton X 100 system
Authors: Dennis Edward A.
Published: May 2005

Physical studies on the formation and structure of mixed micelles of the nonionic surfactant Triton X‐100 and phospholipids and enzymatic studies on the action of phospholipase A2 toward these mixed micelles are presented. Results of nmr intensity, line width, and T1 determinations, as well as gel chromatography and centrifugation experiments on the interaction of Triton X‐100 with egg and dipalmitoyl phosphatidylcholine, are presented and discussed. The structure of mixed micelles is discussed in terms of a working schematic model which is consistent with the experimental results. Kinetic studies on phospholipase A2 (Naja naja) action are then analyzed in terms of this model. The temperature dependence of phospholipase A2 action toward dipalmitoyl phosphatidylcholine is considered in terms of the effect of thermotropic phase transitions on mixed micelle formation. The phospholipase A2‐dipalmitoyl phosphatidylcholine‐Triton X‐100 system is then considered as an artificial model system for studying the effect of lipid phase separations on biological activity.
Nitrate reductase in E. coli: Properties of the enzyme and in vitro reconstitution from enzyme‐deficient mutants
Authors: MacGregor C. H. , Schnaitman C. A.
Published: May 2005

The nitrate reductase of E. coli is an inducible membrane protein with a molecular weight of about 800,000. The enzyme consists of four subunits of 60,000 molecular weight, four subunits of 142,000 molecular weight, four molecules of molybdenum, and nonheme iron. The enzyme may be solubilized by heat extraction, which results from limited digestion by a membrane‐bound protease, or by Triton X‐1 00. When the enzyme is isolated from Triton‐solubilized cytoplasmic membrane by immune precipitation, it contains a third protein of 20,000 molecular weight which may be a cytochrome.

Chlorate resistant (chl) mutants of E. coli lack functional nitrate reductase. Mutants of the classes (chl)and chlB have all of the enzyme polypeptides present in the membrane JI intact form, while in classes chlC and chlE the membrane contains degraded fragments of the polypeptides, suggesting proteolysis of a defective enzyme. Reconstitution of nitrate reductase activity occurs when soluble extracts of various classes of mutants are mixed and incubated at 32°C. This reconstitution requires three things: (a) intact enzyme polypeptides in the form of small soluble lipoprotein fragments resulting from fragmentation of the cytoplasmic membrane during cell breakage; (b) a molybdenum factor which is present in the wild‐type membrane and which accumulates in the cytoplasm of chlB mutants in soluble form; and (c) a soluble factor or enzyme, presumably the chlB gene product, which adds the molybdenum factor to the enzyme

Two conclusions may be drawn from these observations. First, the enzyme is bound t o the membrane by small, hydrophobic regions on one or more of the subunits. Second, the process of reconstitution from mutant extracts is different from the process involved in de novo synthesis of the enzyme in wild‐type E. coli.
Structural changes in myosin during contraction and the state of ATP in the intact frog muscle
Authors: Bárány Michael , Bárány Kate , Burt C. Tyler , Glonek Thomas , Myers Terrell C.
Published: May 2005

The reactivity of myosin to [14C]‐labeled N‐ethylmaleimide ([14C] NEM) or to tritium was determined in functionally different frog muscles. The incorporation of [14C] NEM into myosin decreased during isotonic or isometric contractions, as compared to resting muscle. The cysteine residues which were protected during contraction were not involved in the ATPase activity or the actin‐binding ability of myosin. Peptide mapping revealed that several residues were protected simultaneously. The incorporation of tritium into the peptide N‐H groups of myosin was also decreased during muscle activity. These data support the idea that activation and subsequent contraction of muscle are correlated with structural changes in the myosin molecule.

The reactivity of myosin to [14C] NEM was increased when the muscle was stretched to 140% rest length and treated with iodoacetate to deplete ATP. Based on in vitro experiments and on literature data, it is suggested that in the resting muscle myosin contains bound MgATP which decreases the rate of incorporation of [14C] NEM into myosin and that upon the irreversible loss of ATP the rate increases.

31P nuclear magnetic resonance signals from a number of phosphates were detected in the intact frog muscle. The data indicated that the minimum concentration of ATP in the muscle is 3 mM, a value which agrees with that of chemical determination. The characteristic chemical shifts, coupling constants, and line widths of ATP in the muscle were considerably altered from that of either free ATP in aqueous solutions or ATP in perchloric acid extracts of muscle.
Isotopic probes of catalytic steps of myosin adenosine triphosphatase
Authors: Wolcott Robert G. , Boyer Paul D.
Published: May 2005

A new approach to the direct estimation of the value of the off constant for dissociation of ATP from myosin subfragment 1 (S1) has been developed. From measurements of the extremely slow rate of release of [32P]‐ATP formed from 32Pi by S1 catalysis and the amount of rapidly formed [32P]‐ATP tightly bound to S1, the value of the off constant is approximately 2.8 × 10−4 sec−1 at pH 7.4.

The concentration dependencies for Pi ⇌ H18 OH exchange and for 32Pi incorporation into myosin‐bound ATP give direct measurements of the dissociation constant of Pi from S1. Both approaches show that the enzyme has a very low affinity for Pi, with an apparent Kd of > 400 mM.

Measurement of the average number of water oxygens incorporated into Pi released from ATP by S1‐catalyzed hydrolysis in the presence of Mg2+ suggests that the hydrolytic step reverses an average of at least 5.5 times for each ATP cleaved. With the Ca2+‐activated hydrolysis, less than one oxygen from water appears in each Pi released. This finding is indicative of a possible isotope effect in the attack of water on the terminal phosphoryl group of ATP.
Time‐dependent fluorescence depolarization and lifetime studies of myosin subfragment‐one in the presence of nucleotide and actin
Authors: Mendelson Robert , Putnam Susan , Morales Manuel
Published: May 2005

Time‐dependent fluorescence depolarization and lifetime studies have been made on myosin subfragment 1 to obtain information about mobility changes and dye environment changes when different nucleotides are added. Data are reported for static and actively hydrolyzing systems containing G‐ and F‐actin. Preliminary data indicate that myosin labeled with the fluorophore 1,5 IAEDANS1‐and treated with DTT preserves its actin‐activated Vmax. S1 prepared in this manner gives lifetime changes which are nearly identical for all systems studied. S1 labeling without DTT addition gives a pattern of lifetimes similar, though not identical to ESR work. Either type of labeling produces no observable change in the polarization decay, and we set an upper limit of 15% length change for the elongate S1. An unusually long fluorescence decay lifetime for the S1‐Mg++ ATP‐G‐actin system is found which may indicate a new acto‐S1 state stabilized by G‐actin. The method for obtaining the bound fraction of S1's in the presence of actin is presented and applied to the S1‐F‐actin‐Mg++ ATP system. Qualitative agreement is obtained with other methods.
Studies of substructure and tightly bound nucleotide in bacterial membrane ATPase
Authors: Abrams A. , Jensen C. , Morris D.
Published: May 2005

Highly purified preparations of Streptococcus faecalis ATPase contain a similar but inactive protein detected by prolonged polyacrylamide gel electrophoresis. The inactive protein appears to arise by proteolytic cleavage of the major subunits in the enzyme. By use of a new technique, subunit analysis in SDS gels was performed on the enzyme band and the inactive protein band excised from a polyacrylamide gel after electrophoresis. The results indicated that the ATPase has the composition α3β3γ in which α = 60,000, β = 55,000, and γ = 37,000 daltons. The inactive protein appears to have the composition (f)6 in which f = 49,000 daltons. There is also evidence that the enzyme band contains some slightly modified forms of the ATPase, such as α3β2 (f)γ. The inactive protein lacks the capacity for tight nucleotide binding.

Our experiments show that the tight ATPase‐nucleotide complex formed in S. faecalis cells (the endogenous complex) behaves differently from the tight complex formed in vitro (the exogenous complex). We prepared a doubly labeled complex containing endogenous 32P‐labeled ADP and ATP and exogenous 3H‐labeled ADP. We observed that the addition of free nucelotide to the doubly labeled ATPase displaced the exogenous bound ligand from the enzyme but not the endogenous bound nucleotide. We suggest that the displaceable and nondisplaceable forms of the tight ATPase‐nucleotide complex correspond to two different conformational states of the enzyme.
Interaction of myosin and paramyosin
Authors: Epstein Henry F. , Aronow Bruce J. , Harris Harriet E.
Published: May 2005

The interaction of myosin and paramyosin was investigated by enzymological and ultrastructural techniques. The actin‐activated Mg+2 ATPase of rabbit skeletal muscle myosin can be inhibited by clam adductor paramyosin. Both proteins must be rapidly coprecipitated to form filaments for this inhibition. Slowly formed cofilaments are fully activatable by F‐actin. In both cases, the cofilaments possess unique structural characteristics when compared to homofilaments.

The mode of inhibition appears to be competitive when different concentrations of paramyosin and F‐actin are compared. The apparent affinity of the myosin heads for actin is reduced by the presence of paramyosin within rapidly reconstituted thick filaments. These results suggest that paramyosin may serve as part of a relaxing mechanism within invertebrate muscles. It is unlikely that paramyosin plays a role in the initiation and maintenance of catch within specialized molluscan muscles.
Calcium and magnesium ATPASES of the spectrin fraction of human erythrocytes
Authors: Kirkpatrick F. H. , Woods G. M. , La Celle P. L. , Weed R. I.
Published: May 2005

Using a rapid method of preparation, spectrin has been isolated from human erythrocytes and its ATPase activity investigated. The ATPase activity with calcium has two distinct components, ‐one with optimal activity when calcium and ATP are of equal concentration (low‐Ca‐ATPase) and another which is activated above 1 mM CaCl2 and is maximal at 100 mM CaCl2. There is also a Mg‐ATPase with maximal activity at 10 mM MgCl2. The high‐Ca‐ATPase of spectrin, but not the low‐Ca‐ATPase, is inhibited by magnesium, while the Mg‐ATPase is inhibited by Ca in excess of ATP. None of these activities exhibits the calcium‐stimulated magnesium‐dependent activity characteristic of the red cell calcium pump.
Possible role of firmly bound ATP in the energy transduction of photosynthetic membranes
Authors: Lutz Hans U. , Beyeler Walter , Pflugshaupt Christian , Bachofen Reinhard
Published: May 2005

Chromatophores of Rhodospirillum rubrum and spinach chloroplasts contain firmly bound ATP that is rapidly labeled along with ADP in the presence of 32Pi and endogenous nucleotides. The labeling is not entirely dependent on light. In chloroplasts three types of bound ATP can be defined methodologically by their extraction properties: buffer‐soluble; acid‐soluble; and SDS‐soluble or firmly bound ATP. Extensive washing of the chloroplasts does reduce buffer‐soluble but not acidsoluble and firmly bound APT. Buffer‐soluble [32P] ATP is almost exclusively γ labeled while acid‐soluble and firmly bound ATP are labeled in the β and γ position equally. CCCP, desaspidin, and phlorizin do not inhibit the labeling of firmly bound ATP, whereas the phosphorylation is almost abolished. However, EDTA and NEM pretreatments of the choloroplasts affect both reactions similarly.

The postillumination [32P] ATP synthesis with chromatophores can be inhibited by adding ATP to the incubation mixture after illumination if 32Pi is included only during the dark incubation, but is without effect if 32Pi is present only during illumination. On the other hand, ADP added after illumination inhibits post‐illumination [32P] ATP formation in both chromatophores and chloroplasts only if 32Pi is present during illumination. The data can be explained by a coupling factor having two sites, as proposed previously on the basis that firmly bound ATP does not transfer its phosphoryl group but seems to drive a synthesis of acid‐soluble ATP which incorporates free phosphate (Lutz, H. U., Dahl, J. S., and Bachofen, R.), Biochim. Biophys. Acta 347:359 [1974].
ATP‐stimulated transmitter release and cyclic amp synthesis in isolated chromaffin granules
Authors: Hoffman Philip G. , Zinder Oren , Nikodijevic Olga , Pollard Harvey B.
Published: May 2005

ATP stimulates chromaffin granules from the bovine adrenal medulla to release epinephrine and specific soluble proteins. ATP analogs substituted in the β‐γ‐position with either nitrogen or carbon were also found to be effective at inducing release from isolated chromaffin granules. However, an ATP analog substituted at the α‐β position with carbon was strongly inhibitory. Cyclic AMP was also found to be synthesized by isolated chromaffin granules under release conditions. ATP analogs were effective as substrates for adenylate cyclase in the same order as their efficiency for inducing release from vesicles. Hydrolysis at the β‐γ linkage of ATP therefore is probably not necessary for release; however, hydrolysis at the α‐β position may be important in the release process. Cyclic AMP may be produced and play a regulatory role in this event.
Cooperative properties of hormone receptors in cell membranes
Authors: Meyts Pierre De
Published: May 2005

The binding of many polypeptide hormones to cell surface receptors does not appear to follow the law of mass action. While steady–state binding data are consistent in many cases with either heterogeneous populations of binding sites or interactions of the type known as negative cooperativity, study of the kinetics of dissociation of the hormone receptor complex allows an unambiguous demonstration of cooperative interactions. Negative cooperativity, which seems to be wide‐spread among hormone receptors, provides exquisite sensitivity of the cell at low hormone concentrations while buffering against acutely elevated hormone levels. The molecular mechanisms underlying the cooperativity are still largely unknown. Cooperativity may stem from a conformational transition in individual receptors or involve receptor aggregation in the fluid membrane (clustering) or more extensive membrane phenomena. Thus, new models of hormone action must be considered which integrate the progress in our knowledge of both the complex mechanisms regulating hormone binding to their surface receptors, and the dynamic properties of the cell membrane.
Preliminary characterization of the acetylcholine receptor in human erythrocytes
Authors: Huestis Wray H.
Published: May 2005

The response of human erythrocytes to cholinergic ligands was studied with an electron spin resonance assay. The membrane response to carbamyl choline was found to be antagonized by atropine and, in the absence of calcium, by tetrodotoxin. Experiments with resealed ghosts showed that the membrane response to carbamyl choline required ATP and calcium. Reductive alkylation of intact cells eliminated the cholinergic response, but the presence of saturating amounts of carbamyl choline protected the putative receptor against inactivation. Affinity labeling was used to demonstrate an apparent molecular weight of 41,000 for the carbamyl choline‐binding species. A lipid vesicle extraction technique was used to induce a specific cation permeability defect in intact cells. Preliminary investigation of this phenomenon is described.
Light‐Induced tetracycline accumulation by rhodopseudomonas sphaeroides
Authors: Weckesser Jürgen , Magnuson James A.
Published: May 2005

Light has been used as a primary energy source in studies of tetracycline transport by Rhodopseudomonas sphaeroides. Accumulation of the antibiotic occurs in light, while efflux occurs in dark. Both fluorescence enhancement and radioisotopic tracing have been used to monitor transport. Km's obtained from both techniques are similar. Light‐induced accumulation of tetracyclines is inhibited by a variety of inhibitors, including antimycin A, N‐ethylmaleimide, carbonylcyanide m‐chloro‐phenylhydrazone, and 2,4‐dinitrophenol. A rapid efflux is observed after loading when cells are placed in the dark or treated with inhibitors.
The surface events at fertilization: The movements of the spermatozoon through the sea urchin egg surface and the roles of the surface layers
Authors: Schatten Gerald , Mazia Daniel
Published: May 2005

The sea urchin egg surface at fertilization has been examined with the scanning electron microscope to reveal the movements of the spermatozoon from the exterior, through the surface layer, and into the egg cytoplasm. The layers that the spermatozoon encounter have been studied to determine their physical and chemical natures and their role in early development.

By studying the outside of whole eggs and the inner face of surfaces isolated shorlty after fertlization, it has been possible to complie data on the movements of the spermatozoon through the egg surface. The spermatozoon initially contacts the egg with the elongated acrosomal process. The vitelline sheet, the outermost layer of the egg, separates slightly next to the attached spermatozoon. As membrane from the egg engulfs the spermhead, the cortical granules start to discharge their contents, and a spreading surface deformation, concommitant with a distortion of the fibrous cortex, is initiated. A cluster of elongate microvilli surround the perpendicularly fusing spermatozoon. These microvilli interdigitate as the spermatozoon is forced to lie upon the egg surface between the plasma membrane and the matrix of cortical fibers. The spermatozoon the rotates additionally to enter the egg cytoplasm with the posterior end first; it has rotated 180° through the cell surface. Finally, it detaches into the egg cytoplasm, leaving a scar in the cortex through which it penetrated.

The egg cortex, previously unobserved by electron microscopy, is revealed to be comosed of 50–200 nm fibers. At fertilization they are uniformly organized but during later development this order is lost. The cortex is from 0.2–0.5 μm thick and is a contractile structure.

The role of the outer surface in releasing the cell from the metabolic constraints of the unfertilized egg is shown, and the apparent in the mobilities of the membranes derived from the sperm and the egg are demonstrated. The relation of these layers to the movements of the speratozoon, to the activation of the egg, to the block to polyspermy, and to each other are discussed.
Interactions of neurotoxins with the action potential Na+ ionophore
Authors: Catterall William A. , Ray Radharaman
Published: May 2005

Four neurotoxins that activate the action potential Na+ ionophore of electrically excitable neuroblastoma cells interact with two distinct classes of sites, one specific for the alkaloids veratridine, batrachotoxin, and aconitine, and the second specific for scorpion toxin. Positive heterotropic cooperativity is observed between toxins bound at these two classes of sites. Tetrodotoxin, a specific inhibitor of the action potential Na+ current, inhibits activation by each of these toxins in a noncompetitive manner (KI = 4–8 nM). These results suggest the existence of three functionally separable components of the action potential Na+ ionophore: two regulatory components, which bind activating neurotoxins and interact allosterically in controlling the activity of a third ion‐transport component, which binds tetrodotoxin. The dissociation constant for scorpion toxin binding is increased 10‐fold by depolarization of the cells with K+, suggesting that the scorpion toxin binding site is located on a voltage‐sensitive regulatory component of the ionophore.
The gating currents of sodium channels: Pore‐population‐size effects
Authors: Rayner M. D. , D'Arrigo J. S. , Conquest L. L.
Published: May 2005

Sodium‐channel behavior has been modeled in order to determine the answer to the following question: How large must a population of “on‐off” Sodium pores be before the inherently random behavior of the individual channels becomes smoothed to yield the expected gating current‐conductance relationships which would be predicted from an infinite pore array? Results of this analysis show that for the “opening” situation, an excellent fit was obtained whenever more than about 10 pores were considered. Significant discrepanciesd were observed in the “Closeing” situation, however, for pore arrays of 50 or less. Marked hysteresis is apparent in the behavior of small pore populations.
Structure and control of assembly of cytoplasmic microtubules in normal and transformed cells
Authors: Fuller G. M. , Brinkley B. R.
Published: May 2005

Indirect immunoflurescence analyses using antibodieis directed against 6S tubulin have shown an elaborate cytoplasmic microtubule complex (CMTC) in nontransformed cells in culture. The CMTC is strikingly altered in cells that have been transformed spontaneously by viruses or by chemicals. Assembly of microtubules in vitro and in vivo is markedly inhibited in the presence of elevated levels of calcium. Alteration of the surface of normal cells by brief treatment with low concentrations of trypsin initiate a rapid breakdown of cytoplasmic microtubules. Finally, a hypothesis is presented relating microtubule assembly and surface membrane modulation suggesting that calcium is the primary modulating signal.
Effects of RNase and RNA on in vitro aster assembly
Authors: Zackroff Robert V. , Rosenfeld Arline C. , Weisenberg Richard C.
Published: May 2005

RNase alters the in vitro assembly of spindle asters in homogenates of meiotically dividing surf clam (Spisula solidissima) oocytes. Some effects of RNase, such as reduced astral fiber length, appear nonenzymatic and probably result from RNase binding to tubulin. However, RNase‐induced changes in the microtubule organizing center are also observed. Since other polycations can mimic RNase effects, the existence of an RNA component of the spindle organizing center remains uncertain. Effects of RNase and other polycations on astral fiber length can be prevented and reversed by the RNase inhibitor, polyguanylic acid. Polyguanylic acid can also augment astral fiber length in the absence of added RNase or other polycations. Augmentation by polyguanylic acid is favored by high ionic strength, and can be duplicated by polyuridylic acid and, with less efficiency, by polyadenylic acid. Polucytidylic acid and unfractionated yeast RNA, however, are unable to augment aster assembly. Polyguanylic acid can also augment the length of astral fibers on complete spindles isolated under polymerizing condition. These results demonstrate that specfic polyribonucleotides can alter spindle assembly in vitro. The presence of an inhibitor of microtubule assembly in Spisula oocytes, which can be inactivated by specific RNAs, is suggested.
Energy sources for amino acid transport in animal cells
Authors: Heinz Erich , Geck Peter , Pietrzyk Christian , Burkhardt Gerhard , Pfeiffer Barbara
Published: May 2005

The existence of an electrogenic Na+ pump in Ehrlich cells which substantially contributes to the membrane potential, previously derived from the distribution of the lipid soluble cation tetraphenylphosphonium (TPP+), could be confirmed by an independent method based on the quenching of fluorescence of a cyanine dye derivative, after the mitochondrial respiration had been suppressed by appropriate inhibitors. The mitochondrial membrane potential, by adding to the overall potential as measured in this way is likely to cause an overestimation of the membrane potential difference (p.d.). But since this error tends to diminish with increasing pump activity, the true p.d. of the plasma membrane should easily account for the driving force to drive the active accumulation of amino acids in the absence of an adequate Na+ concentration gradient. Accordingly, the F2‐aminoisobutyric acid (AIB) uptake rises linearly with the distribution of TPP+ at constant Na+ concentrations, suggesting that each responds directly to membrane potential. There is evidence that the electrogenic (free) movement of Cl− is slow, at least at normal p.d., whereas a major part of the Cl− movement across the cellular membrane appears to occur by an electrically silent Cl−‐base exchange mechanism. By such a mode Cl−, together with an almost stoichiometric amount of K+, may under certain conditions move into the cell against a high adverse electrical potential difference. This “paradoxical” movement of K+Cl− contributing to the deviation of the Cl− distribution from the electrochemical equilibrium distribution, is not completely understood. It is insensitive towards ouabain but can almost specifically be inhibited by furosemide. As a likely explanation a H+–K+ exchange pump was previously offered, even though unequivocal evidence of such a pump is so far lacking. According to available evidence the electrogenic movement of free Cl− is too small, at least at normal orientation of the p.d., to significantly shunt the electrogenic pump potential so that the establishment of such a potential is plausible. The evidence presented is considered strong in favor of the gradient hypothesis since even in the absence of an adequate Na+ concentration gradient, the electrogenic Na+ pump will contribute sufficient extra driving force to actively transport amino acid into the cells.