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PubMedDate not supplied

[Extemporaneous histopathological examination in neurosurgery. Report on 500 cases].

The authors review 500 extemporaneous histopathological examinations done in a neurosurgical unit over a 16-month period. The following four questions are asked by the neurosurgeon: is there a tumor? is it a primary or secondary one? what variety is it? what is its degree of malignancy? The percentage of errors was respectively: 2 per cent, 2.2 per cent, 8.8 per cent and 7.4 per cent, or roughly, a percentage two times lower than in a series from the same laboratory done before the use of the low-temperature microtome. It especially seems that the tumoral variety is often determined accurately in meningiomas, neurinomas, medulloblastomas and craniopharyngiomas. In gliomas the variety is often more difficult to accurately affirm, and especially the "grade" of malignancy. The authors analyse the problems raised by the different types of tumors.

Brain Neoplasms↗
PubMed1976

Acetabulaira mediterranea: circadian rhythms of photosynthesis and associated changes in molecular structure of the thylakoid membranes.

Acetabularia mediterranea algae, grown in three different light-dark regimes, were frozen in liquid nitrogen at c.t.(1) 0 and c.t. 6 and a record made of 77 degrees K fluorescence emission spectra of their chloroplasts. Algae grown under LD cycles exhibited a clear circadian rhythm of oxygen production. The low temperature fluorescence emission spectrum at c.t.0 was different from that at c.t.6 and this difference was increased by submitting the algae to successive "freeze-thaw" treatment. Similar results were obtained in DD, and the photosynthesis rhythm remained fully expressed. Algae grown in LL, where no rhythm of photosynthesis could be detected in the samples because there is a great individual variability in period lenght under these conditions, exhibited a similar difference in their low temperature flourescence emission spectra between c.t.0 and c.t.6. We conclude that the circadian rhythm in low-temperature fluorescence emission of the chloroplasts in Acetabularia is related to the circadian rhythm in photosynthesis.

Acetabularia↗
PubMedDate not supplied

[The comparative analysis of interaction between acridine orange and DNA-containing systems].

The interaction between acridine orange (AO) and diluted and concentrated solutions of DNA, DNP systems and chromatin suspension at the physiologic ionic strength was investigated. The effect of AO on DNP systems was also investigated. It was shown that highest possible number of AO molecules bound to DNA made up 70% of the total number of nucleotides. The model of AO binding to DNA is proposed and used for calculation of constants of stronger and weaker AO-binding capacities equal to 6-10(6) M-1 and 1,7-10(5) M-1, respectively. The AO-DNA binding constants in DNP-complex are five as low. The primary number of binding sites in chromatin suspension made up 10% of the corresponding sites in DNA and increased as AO was adsorbed. AO induced the supercontraction of oriented DNP systems at the physiologic ionic strength and the appearance of the low-temperature melting hump.

Acridines↗
PubMedDate not supplied

[Mechanism of photochemical oxidation of bacterioviridin].

The mechanism of bacterioviridin photochemical oxidation has been studied by the methods of ESR, flash-photolysis and low-temperature spectrophotometry. ESR spectrum of pigment cation-radical, a singlet line with H=11 G, g = 2.0027, has been recorded. The bands with maxima at 370, 470, 525, 590, 840 nm correspond to bacterioviridin cation -- radical in the absorption spectra. When -- benzoquinone is used as an electron acceptor with excitation light 640 nm the product of bacterioviridin irreversible oxidation is formed with the absorption band maximum 760 nm and absorption between 350 and 370 nm. It is suggested that this product is of double-oxidized non-radical nature and the mechanism of its formation through oxidation of the pigment cation-radical is discussed. The regeneration reaction of double-oxidized bacterioviridin up to cation-radical form in the presence of triphenylamine as a reducing agent has been carried out. The rate constants of cation-radical decay in the dark and desactivation of triplet state have the following values: K1=(1,64+/-0,15)-10(3) sec-1, K2=(13+/-2,0)-10(3) sec-1 correspondingly. The activation energy of the radical decay in the dark is Eact =(13,2-0,5) kcal/mole.

Bacteriochlorophylls↗
PubMed1992

Radiofrequency gas plasma (glow discharge) disinfection of dental operative instruments, including handpieces.

The radiofrequency-stimulated argon gas plasma (glow discharge) technique, already well-known for surface cleaning and activation of adhesion, was investigated for determination of its separate potential for rapid disinfection of dental operative instruments. Disinfection effectiveness was judged from diminished post-treatment recovery of viable organisms from the instruments agitated in saline. Streptococcus salivarius, Bacillus stearothermophilus, and Escherichia coli were used as primary contaminant organisms, dried from gelatin-thickened laboratory cultures onto the instruments and not subjected to any preliminary cleaning steps. Significant disinfection was obtained, with no sensible temperature increases, in under 10 minutes in laboratory apparatus consuming fewer than 5 Watts of power per cycle. Also, clinically used and deliberately-saliva-contaminated high-speed handpieces were gas-discharge-treated, with their resultant rapid disinfection noted by complete suppression of the viability of any transferred natural contaminant organisms within two minutes. With regard to preservation of instrument quality, it was also shown that this low-temperature gas-discharge method provides the noted substantial disinfection without deterioration of sharp edges. Work now in progress suggests that the method can provide cool, rapid, and complete sterilization when hydrogen peroxide vapors are present in the gas plasma used for treatment of instruments first given the normally recommended thorough pre-cleaning.

Argon↗
PubMedDate not supplied

[Preservation of Pseudomonas putida bacteria at low temperatures].

We have found that the mode of cooling, composition of cryopreservation medium, original concentration of cells and storage temperature affect viability of Pseudomonas putida bacteria during low-temperature preservation. We have elaborated the conditions of preservation, providing for a high survival of bacteria, namely: one-stage cooling with the rates of 30, 40 degrees C/min or immersion into liquid nitrogen in the culturing medium with addition of sucrose, glycerol or dimexide in the concentration of 0.5 M; storage temperature is -80 degrees C divided by -196 degrees C.

Cryopreservation↗
PubMed1992

Multifrequency EPR investigations into the origin of the S2-state signal at g = 4 of the O2-evolving complex.

The low-temperature S2-state EPR signal at g = 4 from the oxygen-evolving complex (OEC) of spinach Photosystem-II-enriched membranes is examined at three frequencies, 4 GHz (S-band), 9 GHz (X-band) and 16 GHz (P-band). While no hyperfine structure is observed at 4 GHz, the signal shows little narrowing and may mask underlying hyperfine structure. At 16 GHz, the signal shows g-anisotropy and a shift in g-components. The middle Kramers doublet of a near rhombic S = 5/2 system is found to be the only possible origin consistent with the frequency dependence of the signal. Computer simulations incorporating underlying hyperfine structure from an Mn monomer or dimer are employed to characterize the system. The low zero field splitting (ZFS) of D = 0.43 cm-1 and near rhombicity of E/D = 0.25 lead to the observed X-band g value of 4.1. Treatment with F- or NH3, which compete with Cl- for a binding site, increases the ZFS and rhombicity of the signal. These results indicate that the origin of the OEC signal at g = 4 is either an Mn(II) monomer or a coupled Mn multimer. The likelihood of a multimer is favored over that of a monomer.

Electron Spin Resonance Spectroscopy↗
PubMedDate not supplied

[Assessment of the quality of relcaimed water by total organic carbon].

The paper discusses possible application of the method of measuring the total content of organic carbon to evaluate the quality or reclaimed water. The paper gives data on the content of organic carbon, ratio of chemical consumption of oxygen and carbon in the atmospheric condensate, urine, condensate of urine low-temperature evaporation and portable water reclaimed from these sources.

Carbon↗
PubMed1977

The photochemical cycle of bacteriorhodopsin.

The reaction cycle of bacteriorhodopsin in the purple membrane isolated from Halobacterium halobium has been studied by optical absorption spectroscopy using low-temperature and flash kinetic techniques. After absorption of light, bacteriohodopsin passes through at least five distinct intermediates. The temperature and pH dependence of the absorbance changes suggests that branch points and/or reversible steps exist in this cycle. Flash spectroscopy in the presence of a pH-indicating dye shows that the transient release of a proton accompanies the photoreaction cycle. The proton release occurs from the exterior and the uptake is on the cytoplasmic side of the membrane, as required by the function of bacteriorhodopsin as a light-driven proton pump. Proton translocating steps connecting release and uptake are indicated by deuterium isotope effects on the kinetics of the cycle. The rapid decay of a light-induced linear dichroism shows that a chromophore orientation change occurs during the reaction cycle.

Bacteriorhodopsins↗
PubMed1979

[Electron acceptors in photosynthetic reaction centers from Rhodopseudomonas spheroides].

Using optical differential spectroscopy and EPR, a parallel study of light-induced electron transfer between the primary (X1) and secondary (X2) quinone-like acceptors in the preparations of reaction centers (RC) isolated from bacterial chromatophore membranes with sodium dodecyl sulfate was carried out. The data from direct measurements of the rate constant temperature dependence for the interaction between light-reduced X1 and X2 (KX1X2) are in good agreement with the data calculated from the kinetic analysis of dark reduction of photooxidized bacteriochlorophyll RC on the acceptors X1 and X2 (KX1X2 = 2.10(-1)S at 20 degrees; Ea = 11,8 kcal.mol-1 within the temperature range of 20 degrees-- -20 degrees). This evidence proves the efficiency of the previously used approach /1, 2/ for the evaluation of the X1-X2 interaction. The method proposed was used for a kinetic analysis of a low-temperature electron transfer from X1 to X2 in RC isolated with lauryldimethylaminoxide (KX1X2 = 2,3.10(2) S-1 at 20 degrees; Ea = 5,5 kcal.mol-1 within the temperature range of 10 degrees-- --70 degrees).

Bacterial Chromatophores↗
PubMedDate not supplied

[Study of structural transformations of the sugar-phosphate chain and nitrogen bases of DNA hydrate by IR-spectroscopy].

The IR-spectra (900-1800 cm-1) of films of native and denatured DNA were studied within the temperature range 4-100 degrees C at different relative humidity (r.h.). Two temperature intervals of S-like change of spectral parameters of absorption bands of sugar-phosphate chain of double-helical DNA are found on temperature relationships at high humidity. These two intervals point to two types of cooperative transitions of sugar-phosphate pattern. The band parameters of nitrous bases are changed only under high temperature transition. In the region of structural transitions of different subsystems of DNA hydrate hyperchromism was wound for the bands of sugar-phosphate chain and hydrate cover unlike hyperchromism specific of most nitrous bases bands. From the data obtained it is proposed to use the basic characteristics of temperature relationship of spectral parameters of the absorption bands of sugar-phosphate pattern and hydrate envelope in the region of low-temperature transition for the "in vivo" analysis of the DNA structure in complex biological systems.

Chemical Phenomena↗
PubMed1979

[Localization of cytochrome b566 at the outer surface of the inner mitochondrial membrane].

The membrane-impermeable protein reagent p-diazonium benzene sulfonate (DABS) inhibits the mitochondrial respiratory chain in the cytochromes b-c1 region. It has been shown that DABS-treatment brings about a dramatic change in a low-temperature absorption spectrum of rat liver mictochondria, so that the long-wavelength alpha-band of ferrocytochrome b566 is sharply decreased, which is indicative of this hemoprotein modification. This observation suggest that cytochrome b566 is accessible to DABS at the outer surface of the coupling mitochondrial membrane.

Animals↗
PubMed1977

The microstructure of isotropic vapor-deposited carbon films.

The structure of thin, vapor-deposited carbon films was characterized by transmission electron microscopy and electron diffraction. Selected area electron diffraction showed very weak and broad peaks, indicating that these carbons contain extremely small crystallites whose dimension in the crystallographic c-direction is about 8 to 10 a. The observed diffraction bands are (h, k, 1 = 0) type reflections, which suggests that individual crystallites consist of graphitic layer planes stacked in parallel groups but with no order between atoms in adjacent planes (turbostratic). The carbon films exhibit no preferred orientation, indicating that the small crystallites are randomly oriented in the film and that the films are therefore isotropic. The measured density (1.8 g/cm3) and the structure of the vapor-deposited carbons are accordingly similar to those of low-temperature isotropic (LTI) pyrolytic carbons.

Carbon↗
PubMedDate not supplied

[Study of the aqueous phase transition in a collagen--water system by the calorimetric and NMR methods].

Heat capacity and line width of proton magnetic resonance of collagen were studied by means of low-temperature calorimatry and high resolution NMR spectroscopy at different values of moisture in the temperature range of ice-water phase transition. Peculiarities of water phase transition in the presence of biopolymers were revealed. It was shown that a definite part of H2O in the "hydration layers" of the macromolecules (0.35 g of H2O/g of protein) is not transformed into ice even at a temperature decrease up to 4 K. The NMR data show that the total mobility of the bound water molecules remains high enough up to the water concentration at which the inner hydration layer of the macromolecule is formed. After the formation of hydrogen-bound water chains in the hydrate layers of collagen the mobility of the bound water molecules decreases.

Calorimetry↗
PubMed1977

Antibody-independent activation of the alternative complement pathway in human serum by parasitic cells.

The lysis of the monocellular parasite Trypanosoma cyclops by normal human serum (NHS) was found to be complement-dependent and to follow activation of the alternative pathway without apparent requirement for conventional antibodies. Lysis of the organisms was inhibited by heat-inactivating NHS at 56 degrees, preincubation of NHS with cobra venom factor or chelation of divalent cations with EDTA. It took place, however, in human C2-deficient serum and was inhibited by prior heating of NHS at 52 degrees to destroy the activity of factor B of the alternative pathway. Moreover, the lytic reaction was magnesium- but not calcium-dependent. Repeated low-temperature (0 degrees) absorption of either human hypogammaglobulinaemic serum or NHS with the parasite failed to remove or significantly decrease their lytic activities.

Complement System Proteins↗
PubMed1977

Frozen preservation of human malignant tumors transplanted into nude mice.

Five transplantable tumors, which originated from human maligant neoplasms and had been maintained in nude mice, were frozen at--70 degrees preserved for 1226 days. Tumor tissue was minced in a mixture of tissue culture medium, 10% dimethyl sulfoxide, and 10% calf serum before freezing. The transplantability of frozen tumors was examined after thawing. Morphological and functional characteristic of each tumor were compared before and after the frozen storage. The results suggest that low-temperature preservation technique can be applied satisfactorily for the maintenance of human malignant tumors which have been maintained by using nude mice.

Animals↗
PubMed1977

[Isolation and characterization of pigment-protein complexes from green serobacteria Chlorobium limicola forma thiosulfatophilum].

A subchromatophore fraction containing the reaction center P-840 was isolated from the chromatophores of green serobacteria Chlorobium limicola forma thiosulfatophilum by ultracentrifugation and its protein composition was characterized. After treatment of the chromatophores by Triton X-100 and subsequent polyacrylamide gel electrophoresis two pigment-protein complex containing bacterioviridin. The proteins of the pigment-protein complex containing bacterioviridin. The proteins of the pigment-protein complexes were obtained. The first complex contained mainly bacteriochlorophyll alpha with bacterioviridin contaminations and the second one-only bacterioviridin. The low-temperature absorption spectrum of the bacteriochlorophyll alpha-containing pigment-protein complex is identical to the absorption spectrum of a water-soluble pigment-protein complex isolated and characterized by Olson and contains proteins with molecular weights of 34.800, 33.100, 27.500 and 23.200. A protein with molecular weight of 32.700 was found in the pigment-protein complexes were compared to the proteins of the photochemically active subchromatophore fraction and chromatophores.

Bacterial Chromatophores↗