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PubMed1978

Radiation damage relative to transmission electron microscopy of biological specimens at low temperature: a review.

When biological specimens are irradiated by the electron beam in the electron microscope, the specimen structure is damaged as a result of molecular excitation, ionization, and subsequent chemical reactions. The radiation damage that occurs in the normal process of electron microscopy is known to present severe limitations for imaging high resolution detail in biological specimens. The question of radiation damage at low temperatures has therefore been investigated with the view in mind of reducing somewhat the rate at which damage occurs. The radiation damage protection found for small molecule (anhydrous) organic compounds is generally rather limited or even non-existent. However, large molecular, hydrated materials show as much as a 10-fold reduction at low temperature in the rate at which radiation damage occurs, relative to the damage rate at room temperature. In the case of hydrated specimens, therefore, low temperature electron microscopy offers an important advantage as part of the overall effort required in obtaining high resolution images of complex biological structures.

Catalase↗
PubMed1979

Low temperature induces decreased germinability of Cylindrocladium microsclerotia.

Numbers of germinable Cylindrocladium crotalariae microsclerotia (assayed at 26 degrees C) decreased progressively over 4 weeks when naturally infested soils were incubated at 6 degrees C. Lower numbers of germinable microsclerotia were obtained from a soil incubated at--3 than at 5 degrees C, while no germinable microsclerotia were found for soils incubated at--10 degrees C. Significantly, when soils incubated at--10 or at 6 degrees C for 4 weeks were transferred to 26 degrees C for 4 weeks, the low-temperature effect was partially reversed. Incubation of naturally infested soils under field conditions from October to February indicated that a similar low-temperature induced phenomenon exists in nature. Germinability of axenic laboratory-grown microsclerotia of C. crotalariae, C. floridanum, and C. scoparium incubated 4 weeks at 6 degrees C ranged from 0 to 91% (mean = 38%) of the initial germinability. Partial recovery of laboratory-grown microsclerotia from the low-temperature effect, by incubation at 26 degrees C, was demonstrated. Conductivity measurements of solutions bathing microsclerotia incubated at 6 degrees C were higher than those incubated at 26 degrees C for 4 weeks and indicated that chilling injury may account, in part, for decreased germinability of microsclerotia.

Cold Temperature↗
PubMed1977

Thermodynamic and conformational studies on an immunoglobulin light chain which reversibly precipitates at low temperatures.

A lambda light chain, isolated from an immunoglobulin G molecule, was found to reversibly precipitate at low temperatures. This cryoprecipitation was a function of pH, ionic strength, protein concentration, and time as well as temperature. The lambda chain underwent a cooperative conformational change as the temperature was lowered from 26 to 0 degrees C as judged by ultraviolet difference spectroscopy and circular dichroism. Normal lambda chains showed no conformational change. By difference spectroscopy it was possible to calculate the equilibrium constant governing the conformational change. The change was strongly exothermic (delta H approximately -80 kcal mol-1) and accompanied by a large decrease in entropy (delta S approximately -280 eu). The midpoint of the transition was dependent on the initial protein concentration, suggesting that only the noncovalent dimer of the lambda chain exhibited the conformational change. The existence of a monomer-dimer eqiulibrium (KA approximately 4 X 10(5) M-1) was confirmed by sedimentation velocity. No conformational change was observed by circular dichroism at concentrations where greater than 95% of lambda chain was in the form of a monomer. Although high ionic strength inhibited cryoprecipitation, it had no effect on the conformational change. Stabilization of the dimer by forming an interchain disulfide bond between two monomers abolished both the conformational change and cryoprecipitation. A fragment corresponding to the constant region was isolated from both peptic and tryptic digests of the lambda chain. This fragment neither cryoprecipitated nor showed temperature dependence conformational changes. It proved impossible to isolate a fragment corresponding to the variable region. Both qualitative and quantitative models are presented to account for the behavior of the lambda chain at low temperatures.

Humans↗
PubMed2025

Low-temperature embryo incubation suppresses off-target mutagenesis during CRISPR-Cas9 genome editing in medaka (Oryzias latipes) and zebrafish (Danio rerio).

Gene knockout using CRISPR-Cas9 is often employed in research aimed at elucidating gene functions in fish. However, CRISPR-Cas9 sometimes introduces unintended alterations, known as off-target mutations. These mutations can reduce the robustness of data during phenotypic analysis. In this study, we focused on the culture temperature, which is known to significantly influence mutagenesis, and examined whether low-temperature culture after introducing CRISPR-Cas9 into early embryos of medaka and zebrafish suppresses off-target mutations. Continuous incubation of medaka at 16 °C significantly reduced off-target mutation rates compared to those at 28 °C; the drawback is that it decreased the survival rate of medaka embryos. Therefore, low-temperature incubation was limited to early development in both zebrafish and medaka, and then the temperature was increased to 28 °C. Under these conditions, the mutation rates of the three off-target regions in medaka (Off-D, Off-P, and Off-A) significantly decreased, whereas those of the three target regions (DJ-1, p4hb, and avt) were unaffected. Similarly, the mutation rate of the zebrafish target region (ywhaqa) remained high, whereas the off-target (Off-Y1) mutation rate significantly reduced. Furthermore, this method effectively suppressed the germ line transmission of off-target mutations in medaka. This approach is effective to obtain more reliable data from the G0 generation of medaka and zebrafish and may reduce the screening effort required to remove individuals with off-target mutations in the F1 generation.

Animals↗
PubMedDate not supplied

Rapid adaptation to neuronal membrane effects of ethanol and low temperature: some speculations on mechanism.

There is increasing evidence that ethanol exerts its primary effect at neuronal membranes by influencing specific lipid--protein or lipid--lipid interactions that control the state of organization of a specific membrane component; for example, a specific lipid--protein complex that controls a particular physiological property. This implies that tolerance to ethanol is the result of a change in the composition and/or state of organization of this critical membrane component. This altered state confers ethanol resistance. It may or may not have an effect on function in the absence of ethanol. One basis for these speculations comes from experiments using a sensitive and specific neurophysiological assay -- the rate of decay of posttetanic potentiation (PTP) at an identified synapse in an isolated, perfused Aplysia ganglion. We review evidence that PTP decay rate is strikingly accelerated by ethanol (a membrane-fluidizing agent) and strikingly decelerated below a transition temperature, presumably reflecting a transition in the structure of a membrane component. The ethanol and low-temperature effects are antagonistic. The system develops adaptation (tolerance) to either ethanol or low temperature within hours of its exposure. Tolerance persists for at least 12 hours, the longest interval tested thus far. In the absence of ethanol and at normal temperature the system behaves normally, that is it shows no "physical dependence". The system also has the remarkable property that when it becomes tolerant to either of these treatments, it shows tolerance to the other treatment that normally has the opposite effect. Therefore, the adaptation to either treatment cannot be a simple change in membrane composition governing overall membrane fluidity. A hypothesis which could explain the bidirectional cross-tolerance is considered in which adaptation to both treatments involves a shift from a homogeneous to a more heterogeneous composition of the critical membrane component, for example increasing heterogeneity in boundary lipid surrounding a critical membrane protein. It is becoming increasingly clear that ethanol exerts its primary effect by altering cell membrane structure -- by "fluidizing" or expanding neuronal and other membranes [1 - 6]. This effect results when ethanol, a somewhat hydrophobic molecule, intercalates between some fatty acid chains of membranes, reducing the degree of order of their alignment and increasing the lateral mobility of some membrane components. Decrease in the order of the fatty acid chains results in a measurable expansion of the membrane; and the change in fluidity is reflected in the change in mobility of appropriate probes that can be dissolved in the membrane [6, 7]. It is presumed that the physiological effects of ethanol are consequences of its fluidization of some critical membrane components; and that tolerance to ethanol is based on some form of resistance to this fluidization...

Animals↗
PubMed1979

Enzyme immobilization by radiation-induced polymerization of hydrophobic glass-forming monomers at low temperatures.

Enzyme immobilization was studied by means of radiation-induced polymerization of hydrophobic glass-forming monomers at low temperatures. The polymerized hydrophobic composite was generally obtained in microspheric form. Enzymatic activity showed little decrease with repeated use in these systems. The particle size of the microsphere increased with increasing monomer concentration, and activity yield had a maximum at an optimum monomer concentration. Immobilization by copolymerization of hydrophilic and hydrophobic comonomers was also investigated and a maximum activity yield was found at a certain monomer concentration. A model scheme for immobilization at low temperatures was proposed and discussed.

Carbohydrate Epimerases↗
PubMedDate not supplied

[Investigation of the recombination kinetic of photodissoziated myoglobin-CO at low temperatures by Mössbauer spectroscopy (author's transl)].

Myoglobin-CO (MbCO) has been photodissoziated with white and monochromatic light at low temperatures (5--40 degrees K). The photoproduct Mb* was identified with Mössbauer spectroscopy as ferrous high-spin complex, with isomer shift and quadrupole splitting, which are similar to the corresponding parameters of deoxymyoglobin. From the time-dependent change of the linewidth of the Mb*-Mössbauer-spectrum at 5 degrees K over a time-intervall of 7 hours we conclude, that there exist several slightly different Mb*-conformations with different recombination characteristics. In order to obtain a convenient time resolution of the recombination behavior, we investigate the time-dependence of one of the Mb*-absorptionlines with a Mössbauer drive of constant velocity. The resulting recombination data then are analyzed in various steps of approximation. It is shown that at least two independent exponentials are necessary for the interpretation of experimental data. The attempt to interprete the experimental data on the basis of distribution of energies is in qualitative agreement with corresponding results, which are derived from optical recombination data by Austin et al. Typical activation energies for the recombination process CO leads to Mb* are 2 kcal/mol. At low temperature (T less than 46 degrees K) the recombination behavior is explained by quantum-mechanical tunneling.

Carbon Monoxide↗
PubMed1976

Light-induced absorption changes in photosystem I at low temperatures.

Light-induced absorption changes associated with the primary photochemical reaction and dark relaxation in Photosystem I were measured at various low temperatures. A possible temperature-dependent long-range electron tunneling process was suggested to account for the unique temperature dependence of the dark decay process. The kinetics of the light-induced absorption changes are in good agreement with the light-induced EPR changes reported earlier (Ke, B., Sugahara, K., Shaw, E.R., Hansen, R. E., Hamilton, W. D. and Beinert, H. (1974) Biochim, Biophys. Acta 368, 401--408) for the same Photosystem I subchloroplast fragment at comparable temperatures. All absorption changes between 400 and 725 nm at 86degreesK have identical kinetics. The light-minus-dark difference spectrum is very similar to that of P-700 at room temperature, with an additional prominent positive change at 690 nm. Possible contributions by P-430 to the blue and red spectral changes were discussed. It was demonstrated that the intensity of the measuring beam has a drastic effect on the light-induced absorption changes of Photosystem I at low temperatures. Various pretreatments of the Photosystem I fragments such as those that photochemically (or chemically) oxidize the primary donor or photoreduce the primary acceptor abolish the subsequent photochemical reaction. Continuous illumination of the Photosystem I fragments before and during freezing has the same effect. In the temperature range of --20 to --60degreesC, an unusual counter absorption change as well as a counter EPR change were observed.

2,6-Dichloroindophenol↗
PubMed1978

Photochemical reactions of cytochrome oxidase at low temperatures.

The unique of CO-cytochrome oxidase as first noted by Yonetani et al. (22) is that after its photodissociation at low temperatures recombination occurs as the sample temperature is raised, but at temperatures considerably higher than those for other CO-heme and CO-hemoprotein complexes; that is, the half recombination temperature is 180 K contrary to 25-30 K for other CO complexes. The photodissociability, however, disappeared when monomeric cytochrome oxidase was treated with pCMB to remove an intrinsic copper, the significance of which in CO complex formation was thus demonstrated. It is proposed that the copper is situated close to heme a and traps the photodissociated CO. The access of the trapped CO to the heme a to resume the original binding is effected only when sufficient energy for thermal agitation is provided by elevating the sample temperature. During the course of this study, new photo- and thermochromic properties were observed with the reduced enzyme by cooling it in liquid nitrogen after preincubation at pH 8.6 to 10.5. The characteristic bands appeared at 575 and 428 nm and diminished when this ample was illuminated at 26 K. As the sample temperature was raised these bands were restored with a half transition temperature of 80 K. When the reduced oxidase had been complexed with CO, cyanide or azide, or treated with pCMB, such a unique species did not appear. The enthalpy change of 1.16 kcal/mol for the formation of this species as well as the above-described properties suggests that the hydrogen bond between the formyl side group of heme a and one of seven sulfhydryl groups in cytochrome oxidase is responsible for the appearance and disappearance of this new species. Based on these results a schematic model has been proposed for the photo- and thermochromism of cytochrome oxidase at cryogenic temperatures and for the microenvironment of the prosthetic heme a and copper in this enzyme. On the other hand, contrary to the central dogma of Warburg that all CO-heme and CO-hemoprotein complexes are photodissociable, we observed little photodissociability with some CO-heme complexes, especially at very low temperatures, and presented a view that depending on the bond type between CO and heme iron the efficiency of photodissociation is so varied that under certain conditions practically no photodissociation occurs. According to this view a tilted arrangement of the ligated CO towards the heme plane accompanying a large extent of overlapping of the dpi(Fe) and the pi* antibonding orbital on the CO facilitates photodissociation. In addition to our own observations of photochemical properties of cytochrome oxidase and heme model compounds, recent photodynamic studies carried out by other investigator on CO-heme and CO-hemoproteins are summarized and the validity and limitation of their models are discussed.

Carbon Monoxide↗
PubMed1978

Paramagnetic and crystallographic effects of low temperature ashing on human bone and tooth enamel.

Low temperature ashing by excited gas (LTA) causes crystallographic and paramagnetic alterations of the human bone and tooth enamel mineral. On the one hand, LTA induces variations of the alpha lattice parameter. These variations depend upon the nature of the gas used, but are little affected by its degree of excitation. Trapping of gas molecules in the crystal structure is demonstrated. On the other hand, LTA produces two preponderant paramagnetic centers in bone and enamel samples at 20 degrees C. Their inorganic origin clearly indicated. One of the two radicals has been identified as O3- (g1 = 2.002, g2 = 2.010, g3 = 2.016) and the other as (CO3-3 (parallel = 1.996, g = perpendicular 2.003). Variations of the alpha lattice parameter and trapping of paramagnetic gas species do not seem to be directly related.

Apatites↗
PubMed1978

Effect of low temperature on the membrane currents and tension components of bullfrog atrial muscle.

In order to clarify the nature of inotropic action of low temperature, the effects of cooling on the membrane currents and tension components were studied on the bullfrog atrial muscle under voltage clamped and unclamped conditions with double gap method. Cooling (in between 35 degrees-7 degrees C) produced an increase of overshoot and a prolongation of the action potential accompanied by a slight depolarization of the membrane, a decrease of basal tension and an increase of twitch contraction. Under voltage clamp, a marked augmentation of contraction also occurred despite a decrease of basal tension, suggesting that the inotropic effect of cooling is not merely dependent on the prolongation of action potential. When the components of membrane current and tension were isolated in modified Ringer solutions, it became clear that ICa and ICa -dependent tension markedly increased at low temperature, while all other currents (INaf, INas, IK1 Ix) and ICa-independent tension decreased. Leaky membrane current (I1) for hyperpolarizing pulses also diminished. Temperature coefficient (Q10) of the ICa-independent tension component was 1.2-1.5 between 7 degrees C and 17 degrees C, while that of ICa-dependent tension varied depending on depolarization voltages. These data were discussed in relation to possible alteration of Ca concentration at outer and inner layers of the membrane which may depend on temperature.

Action Potentials↗
PubMed1978

The role of hormones in the acclimation of fish to low temperatures.

The known cases elucidating the role of hormones in the regulation of physiological and biochemical changes which occur when fish are acclimated to low temperatures are sparse, but evidence is accumulating to implicate prolactin, glucagon, insulin and perhaps thyroxine and cortisol in at least some of the physiological adjustments observed in some species. The need for further research on hormonal control mechanisms at work during low-temperature acclimation is discussed, with special emphasis placed on neuroendocrine relationships.

Adaptation, Physiological↗
PubMed1975

Studies on the charge transfer band in high spin state of ferric myoglobin and hemoglobin by low temperature optical and magnetic circular dichroism spectroscopy.

The behavior of charge transfer band, appearing at 600-650 nm in ferric high spin derivatives of myoglobin and hemoglobin, was studied under various conditions by low temperature optical and magnetic circular dichroism spectroscopy. Optical absorption spectra have demonstrated that: (1) The charge transfer band at 630 nm of myoglobin (Fe3+)-H2O (pH 7.0) at room temperature split into three bands, 627 nm, 645 nm and 664 nm (shoulder) at 77 degrees K, whereas that of hemoglobin (Fe3+)-H2O showed no splitting. (2) By lowering the pH value from 7.5 to 4.3 this splitting in myoglobin was observed to disappear only in the presence of a small amount of phosphate ion, accompanying a midpoint at pH 6.7 +/- 0.1. This does not originate from the released hemin. (3) Hemin (pH 7.55) showed no splitting of the charge transfer band at 77 degrees K. (4) This splitting depended on the species of 6th ligand. For myoglobin-F- the splitting could scarcely be observed, whereas the proton-donating ligands such as HCOOH and CH3OH exhibit the splitting as well as H2O. Magnetic circular dichroism spectra have demonstrated that: (5) The charge transfer band at 600-500 nm indicated Faraday A term and B term. (6) A negative B term band was observed at 650 nm for myoglobin-H2O in the glassic solvent of potassium glycerophosphate-glycerol, whereas it was not observed for hemoglobin-H2O. Several discussions were performed on the origin of splitting of the charge transfer band in myoglobin-H2O. It is now concluded that the hydrogen bond between the 6th ligand and the distal histidine contributes to the splitting of the charge transfer band around 630 nm for myoglobin Fe3+)-H2O at low temperature and that disappearance of the splitting at low pH is originated from the presence of phosphate ion.

Adult↗
PubMed1979

The reaction of cytochrome omicron in Escherichia coli with oxygen. Low-temperature kinetic and spectral studies.

1. The reactions of cytochrome omicron in intact cells of aerobically grown Escherichia coli with O2 and CO have been studied at low temperature. 2. Flash photolysis of CO-liganded cells in the presence of O2 and at temperatures between -79 and -102 degrees C results in the oxidation of kinetically heterogeneous beta-type cytochromes (including cytochrome omicron), but not of cytochrome d. 3. The reaction of reduced cytochrome omicron with O2 involves O2 binding to give intermediate(s) with spectral characteristics similar to that of the reduced oxidase-CO complex. Observation in the alpha-region suggests that unexplained ligand dissociation accompanies the initial O2 binding. 4. At temperatures below -98 degrees C, an 'end point' in the reaction is reached; further reaction and oxidation of cytochrome omicron occurs on raising the temperature. 5. There is a linear relationship between the rate of formation of the oxygen compound and the O2 concentration up to 0.5 mM. The second-order constant for its formation (k+1) is 0.91 M-1.S-1 at -101 degrees C. The reaction is not readily reversible, the value of k-1 being 1.4 X 10(-5) S-1 and the kd 1.5 X 10(-5) M. 6. The energy of activation for this reaction at low temperatures is 29.9kJ (7.1 kcal)/mol. 7. The reaction with O2 is distinguished from that with CO by the markedly lower velocity and high photolytic reversibility of the latter. 8. Comparisons are drawn between the intermediate(s) in the O2 reaction of cytochrome omicron in E. coli and those identified in other bacteria and in the reaction of cytochrome aa3 with O2.

Carbon Monoxide↗
PubMed1976

Low temperature magnetic circular dichroism spectra of met- and myoglobin derivatives.

1. Low temperature magnetic circular dichroism spectra of high and low spin derivatives of metmyoglobin and myoglobin have been measured in the Soret and high wavelength regions. 2. The large difference in intensity of the Soret magnetic circular dichroism bands suggest that a correlation exists between the signal intensity and spin state of the heme-iron. 3. From a comparison of the high and low spin sepctra of the myoglobin derivatives it is concluded that oxymyoglobin contains between 10 and 20% of a ferrous high spin component below 100 degrees K.

Animals↗
PubMed1977

Cardiac adrenoceptors at low temperature: what is the experimental evidence for the adrenoceptor interconversion hypothesis?

Isolated heart preparations of frog and rat were used to test the validity of the adrenoceptor interconversion hypothesis. This hypothesis claims that low temperature converts the inotropic beta-adrenoceptors in isolated frog and rat heart to alpha-adrenoceptors. The present results do not support the adrenoceptor interconversion hypothesis. In the isolated frog ventricle, lowering the temperature from 24 C to 14 C did not significantly alter the inotropic potency of the sympathomimetic drugs isoprenaline, epinephrine, and phenylephrine and did not reduce the potency of the beta-adrenoceptor blocking drug propranolol as an epinephrine antagonist. In the isolated rat left atrium, lowering the temperature from 31 C to 17-19 C did not significantly change the inotropic potency of isoprenaline, norepinephrine and phenylephrine, did not diminish the potency of propranolol, and did not increase the potency of the alpha-adrenoceptor blocking drug phentolamine.--Benfey, B. G. Cardiac adrenoceptors at low temperature; what is the experimental evidence for the adrenoceptor interconversion hypothesis?

Animals↗