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  • PACS. 75.30.Et Exchange and superexchange interactions - 75.30.Kz Magnetic phase boundaries (including magnetic transitions, metamagnetism, etc.) - 75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)  (2)
  • Pisum  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    Effect of palmitoylcarnitine on mitochondrial activities (1995)
    Springer
    Planta 196 (1995), S. 720-726 
    Details
    ISSN: 1432-2048
    Keywords: β-Oxidation ; Mitochondrion ; Palmitoylcarnitine ; Pisum ; Solanum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Mitochondria from pea (Pisum sativum L.) cotyledons and potato (Solanum tuberosum L.) tubers exhibited a palmitoyl carnitine-dependent, KCN-sensitive stimulation of the oxygen uptake measured in the presence of 0.2mmol·−1 malate (sparker malate), provided a certain concentration range of palmitoylcarnitine was observed. Above this concentration range, which was dependent on the bovine serum albumin (BSA) concentration of the reaction mixture, the mitochondrial oxygen uptake was inhibited by palmitoylcarnitine. Palmitoylcarnitine (racemate) and palmitoyl-l-carnitine were equally effective in stimulating/inhibiting mitochondrial oxygen uptake in the presence of sparker malate. The mitochondrial membrane potential generated in the presence of sparker malate was partially dissipated by palmitoyl-lcarnitine concentrations stimulating the mitochondrial oxygen uptake. The formation of acid-soluble radioactivity in reaction mixtures provided with [1-14C]palmitoyll-carnitine was considerably lower than that expected minimally if the palmitoyl-l-carnitine-stimulated oxygen uptake resulted from palmitoyl-l-carnitine oxidation sparked by malate. Palmitoylcarnitine concentrations resulting in stimulation of the mitochondrial oxygen uptake in the presence of sparker malate also led to a stimulation of succinate-cytochrome c reductase activity, as well as to an increase in the measurable activities of mitochondrial matrix enzymes, indicating loss of both mitochondrial integrity and mitochondrial enzyme latency in the presence of palmitoylcarnitine. Correspondingly, malate-dependent NADH formation was stimulated by palmitoylcarnitine. Neither NAD reduction nor oxygen uptake were observed when the mitochondria were provided with palmitoylcarnitine only. The oxygen uptake due to glycine oxidation by mitochondria from green sunflower (Helianthus annuus L.) cotyledons was affected by palmitoylcarnitine in a similar manner to the oxygen uptake of pea cotyledon and potato tuber mitochondria in the presence of sparker malate. The results lead to the conclusion that the palmitoylcarnitine-dependent stimulation of mitochondrial oxygen uptake observed in the presence of sparker malate results substantially from an enhanced malate oxidation due to the detergent effect of palmitoylcarnitine on the mitochondrial membranes, rather than from palmitoylcarnitine β-oxidation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00197337
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of palmitoylcarnitine on mitochondrial activities (1995)
    Springer
    Planta 196 (1995), S. 720-726 
    Details
    ISSN: 1432-2048
    Keywords: β-Oxidation ; Mitochondrion ; Palmitoylcarnitine ; Pisum ; Solanum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Mitochondria from pea (Pisum sativum L.) cotyledons and potato (Solanum tuberosum L.) tubers exhibited a palmitoyl carnitine-dependent, KCN-sensitive stimulation of the oxygen uptake measured in the presence of 0.2mmol·−1 malate (sparker malate), provided a certain concentration range of palmitoylcarnitine was observed. Above this concentration range, which was dependent on the bovine serum albumin (BSA) concentration of the reaction mixture, the mitochondrial oxygen uptake was inhibited by palmitoylcarnitine. Palmitoylcarnitine (racemate) and palmitoyl-l-carnitine were equally effective in stimulating/inhibiting mitochondrial oxygen uptake in the presence of sparker malate. The mitochondrial membrane potential generated in the presence of sparker malate was partially dissipated by palmitoyl-lcarnitine concentrations stimulating the mitochondrial oxygen uptake. The formation of acid-soluble radioactivity in reaction mixtures provided with [1-14C]palmitoyll-carnitine was considerably lower than that expected minimally if the palmitoyl-l-carnitine-stimulated oxygen uptake resulted from palmitoyl-l-carnitine oxidation sparked by malate. Palmitoylcarnitine concentrations resulting in stimulation of the mitochondrial oxygen uptake in the presence of sparker malate also led to a stimulation of succinate-cytochromec reductase activity, as well as to an increase in the measurable activities of mitochondrial matrix enzymes, indicating loss of both mitochondrial integrity and mitochondrial enzyme latency in the presence of palmitoylcarnitine. Correspondingly, malate-dependent NADH formation was stimulated by palmitoylcarnitine. Neither NAD reduction nor oxygen uptake were observed when the mitochondria were provided with palmitoylcarnitine only. The oxygen uptake due to glycine oxidation by mitochondria from green sunflower (Helianthus annuus L.) cotyledons was affected by palmitoylcarnitine in a similar manner to the oxygen uptake of pea cotyledon and potato tuber mitochondria in the presence of sparker malate. The results lead to the conclusion that the palmitoylcarnitine-dependent stimulation of mitochondrial oxygen uptake observed in the presence of sparker malate results substantially from an enhanced malate oxidation due to the detergent effect of palmitoylcarnitine on the mitochondrial membranes, rather than from palmitoylcarnitine β-oxidation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01106766
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  • 3
    Electronic Resource
    Electronic Resource
    On the T Bloch law in magnets with fourth-order exchange interaction (1999)
    Springer
    The European physical journal 8 (1999), S. 207-216 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 75.30.Et Exchange and superexchange interactions - 75.30.Kz Magnetic phase boundaries (including magnetic transitions, metamagnetism, etc.) - 75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: For the ferromagnets EuS and GdMg, in which fourth-order exchange interactions (i.e. biquadratic, three-spin and four-spin interactions) have been identified, the deviation of the spontaneous magnetization with respect to the T =0 value is shown to follow a T2 law instead of the famous T3/2 law expected for a Heisenberg ferromagnet. Moreover, the observed T2 law holds for temperatures as large as 0.8TC and the extrapolated magnetization value for does not conform to ferromagnetic saturation. This is because the fourth-order exchange interactions generate a second order-parameter which is assumed to govern the order of the transverse moment components. These moment components have a finite expectation value for at the expense of the Heisenberg order parameter. Like the spontaneous magnetization, the critical field curves B c ( T ) of the metamagnet EuSe and the antiferromagnet EuTe also start decreasing with a T2 term for . It is argued that the T2 law is a consequence of the fourth-order exchange interactions. This is shown experimentally by a study of the critical field curves [0pt] pertinent to the longitudinal (Heisenberg) order-parameter in the diamagnetically diluted antiferromagnets EuxSr1-xTe. In this solid solution series a particular composition of x c =0.85 exists at which the different fourth-order interaction processes compensate each other in the high temperature average. As a consequence, an EuxSr1-xTe sample with x =0.85 meets the requirements of a Heisenberg antiferromagnet at least if a quantity is considered for which the high-temperature average over all fourth-order interactions is decisive. This seems to be the case for the critical field curve [0pt] which gives the phase boundary to the paramagnetic phase. In fact, a crossover from a T2 to a T3/2 law is observed for [0pt] on approaching xc. This, we believe, shows the frequently observed T2 law is caused by the fourth-order interactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510050683
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  • 4
    Electronic Resource
    Electronic Resource
    Investigations of the sublattice magnetizations M (T) in antiferromagnets with fourth-order exchange interactions: Eu Sr Te (1999)
    Springer
    The European physical journal 8 (1999), S. 217-224 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 75.30.Et Exchange and superexchange interactions - 75.30.Kz Magnetic phase boundaries (including magnetic transitions, metamagnetism, etc.) - 75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We present a neutron scattering study of the temperature and composition dependence of the MnO-type superstructure reflection intensities in the diamagnetically diluted antiferromagnetic compounds EuxSr1-xTe. In these materials antiferromagnetic biquadratic and ferromagnetic three-spin interactions have been identified recently. These fourth-order non-Heisenberg interactions are able to create their own order parameter which is believed to govern the order of the transverse moment components and which, hence, is directed perpendicular to the common Heisenberg order parameter. The observed MnO-type diffraction intensities originate in the sublattice magnetizations, , of both order parameters. Due to the different composition dependencies for biquadratic interaction processes and three-spin interaction processes , the ferromagnetic three-spin interactions dominate for x 〉 x c =0.85, while for x 〈0.85 the antiferromagnetic biquadratic interactions dominate. Associated with this sign change in the fourth-order interaction sum the transverse order parameter changes from the antiferromagnetic MnO type for x 〈0.85 to ferromagnetic for x 〉0.85. This is noticed as a sudden decrease of the low-temperature MnO scattering intensities at x c =0.85. Although susceptibility measurements reveal clearly a ferromagnetic component for x 〉0.85 no ferromagnetic Bragg intensities were observed in standard neutron scattering spectra using EuTe powder samples. We explain this by the competition of antiferromagnetic biquadratic and ferromagnetic three-spin interactions whereby a disturbed ferromagnetic superstructure may be generated which gives rise also to weak MnO-type diffraction lines. It is found that the resulting obeys a T2 law until a temperature as large as 0.75TN irrespective of the nature of the transverse order parameter. The T2 law must, hence, be common to both types of order parameter showing that the fourth-order interactions re-define the spin dynamics of both completely. From the linear composition dependence of the normalized T2 coefficient the existence of three-spin interactions is again confirmed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510050684
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