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Biomedical subjects

A Frolov

Publications and source records attributed to A Frolov.

17 recordsLinked to original sources
PubMed1999

Isolation and identification of a mouse brain protein recognized by antisera to heart fatty acid-binding protein.

Although a novel brain-specific fatty acid-binding protein (B-FABP) was recently cloned, the identity of a second fatty acid-binding protein detected with antibodies to the heart (H-FABP) has not been clearly resolved. The present investigation, using matrix-assisted laser desorption mass spectrometry, showed that this protein was a form of H-FABP whose N-terminal amino acid was neither methionine nor was it acetylated. Furthermore, isoelectric focusing revealed two major isoforms, a major band pl 7.4 and a minor band pl 6.4, in a distribution pattern opposite to that observed for H-FABP in the heart. Tryptic peptide mass maps of the in-gel digested SDS polyacrylamide gel electrophoresis protein bands showed that the two isoforms differed only in a single peptide corresponding to residues 97-106 of the heart H-FABP sequence. This peptide had an [M + H]+ ion of either 1205.62 (pl 7.4) or 1206.53 (pl 6.4), consistent with a single amino acid substitution, Asp98 or Asn98. Whereas it is well established that both H-FABP and B-FABP interact with polyunsaturated fatty acids, we showed that they also significantly alter plasma membrane cholesterol dynamics in a manner opposite to that of another brain lipid-binding protein, sterol carrier protein-2. In summary, the data demonstrated for the first time that the H-FABP from brain, while nearly identical to H-FABP from heart, differed significantly in isoform distribution and in amino terminal structure from heart H-FABP. This suggests that the brain and heart H-FABP may not necessarily function identically in these tissues.

Amino Acid Sequence↗
PubMed1999

Cellular uptake and intracellular trafficking of long chain fatty acids.

While aspects of cellular fatty acid uptake have been studied as early as 50 years ago, recent developments in this rapidly evolving field have yielded new functional insights on the individual mechanistic steps in this process. The extremely low aqueous solubility of long chain fatty acids (LCFA) together with the very high affinity of serum albumin and cytoplasmic fatty acid binding proteins for LCFA have challenged the limits of technology in resolving the individual steps of this process. To date no single mechanism alone accounts for regulation of cellular LCFA uptake. Key regulatory points in cellular uptake of LCFA include: the aqueous solubility of the LCFA; the driving force(s) for LCFA entry into the cell membrane; the relative roles of diffusional and protein mediated LCFA translocation across the plasma membrane; cytoplasmic LCFA binding protein-mediated uptake and/or intracellular diffusion; the activity of LCFA-CoA synthetase; and cytoplasmic protein mediated targeting of LCFA or LCFA-CoAs toward specific metabolic pathways. The emerging picture is that the cell has multiple, overlapping mechanisms that assure adequate uptake and directed intracellular movement of LCFA required for maintenance of physiological functions. The upcoming challenge is to take advantage of new advances in this field to elucidate the differential interactions between these pathways in intact cells and in tissues.

Biological Transport↗
PubMed1998

Acyl coenzyme A binding protein. Conformational sensitivity to long chain fatty acyl-CoA.

Cellular unbound long chain fatty acyl-CoAs (>14 carbon) are potent regulators of gene transcription and intracellular signaling. Although the cytosolic acyl-CoA binding protein (ACBP) has high affinity for medium chain fatty acyl-CoAs, direct interaction of ACBP with >14-carbon fatty acyl-CoAs has not been established. Steady state, photon counting fluorescence spectroscopy directly established that rat liver ACBP bound 18-carbon cis- and trans-parinaroyl-CoA, Kd = 7.03 +/- 0.95 and 4.40 +/- 0.43 nM. Time-resolved fluorometry revealed that ACBP-bound parinaroyl-CoAs had high rotational freedom within the single, relatively hydrophobic (epsilon <32), binding site. Tyr and Trp fluorescence dynamics demonstrated that apo-ACBP was an ellipsoidal protein (axes of 15 and 9 A) whose conformation was altered by oleoyl-CoA in the holo-ACBP as shown by a 2-A decrease of ACBP hydrodynamic diameter and increased Trp segmental motions. Thus, native liver ACBP binds >14-carbon fatty acyl-CoAs with nanomolar affinity at a single binding site. Acyl-CoA-induced conformational alterations in ACBP may be significant to its putative functions in lipid metabolism and regulation of processes sensitive to unbound long chain fatty acyl-CoAs.

Acyl Coenzyme A↗
PubMed1998

Axial synergies during human upper trunk bending.

Upper trunk bending movements were accompanied by opposite movements of the lower body segments. These axial kinematic synergies maintained equilibrium during the movement performance by stabilizing the center of gravity (CG), which shifted on average across all the subjects by 1 +/- 4 cm in the anteroposterior direction and thus always remained within the support area. The aim of the present investigation was to provide an insight into the central control responsible for the performance of these synergies. The kinematic analysis was performed by the method of principal components (PC) analysis applied to the covariation between ankle, knee and hip joint angles and compared with CG shifts during upper trunk bending. Subjects were asked to perform backward or forward upper trunk bending in response to a tone. They were instructed to move as fast as possible or slowly (2 s), with high or low movement amplitudes. PC analysis showed a strong correlation between hip, knee and ankle joint changes. The first principal component (PC1) representing a multijoint movement with fixed ratios between joint angular changes, accounted, on average, for 99.7% +/- 0.2% of the total angular variance in the forward trunk movements and for 98.4% +/- 1.4% in the backward movements. The instructed voluntary regulation of the amplitude and velocity of the movement was achieved by adapting the bell-shaped profile of the velocity time course without changes in interjoint angular relations. Fixed ratios between changes in joint angles, represented by PC1, ensured localization of the CG within the support area during trunk bending. The ratios given by PC1 showed highly significant dependence on subjects, suggesting the adaptability of the central control to each subject's biomechanical peculiarities. Subject's intertrial variability of PC1 ratios was small, suggesting a stereotyped automatic interjoint coordination. When changing velocity and amplitude of the movement, the ratios remained the same in about half the subjects while in others slight variations were observed. A weak second principal component (PC2) was shown only for fast movements. In forward movements PC2 reflected the early knee flexion that seems related to the disturbances caused by the passive interaction between body segments, rather than to the effect of a central command. In fast backward movements, PC2 reflected the delay in hip extension relative to the movement onset in the ankle and knee that mirrors intersubject differences in the initiation process of the axial synergy. The results suggest that PC1 reflects the centrally controlled multijoint movement, defining the time course and amplitude of the movement and fixing the ratios between changes in joint angles. They support the hypothesis that the axial kinematic synergies result from a central automatic control that stabilizes the CG shift in the anteroposterior direction while performing the upper trunk bending.

Adaptation, Physiological↗
PubMed1998

Fatty acid binding protein isoforms: structure and function.

Although structural aspects of cytosolic fatty acid binding proteins (FABPs) in mammalian tissues are now well understood, significant advances regarding the physiological function(s) of these proteins have been slow in forthcoming. Part of the difficulty lies in the complexity of the multigene FABP family with nearly twenty identified members. Furthermore, isoelectric focusing and ion exchange chromatography operationally resolve many of the mammalian native FABPs into putative isoforms. However, a more classical biochemical definition of an isoform, i.e. proteins differing by a single amino acid, suggests that the operational definition is too broad. Because at least one putative heart H-FABP isoform, the mammary derived growth inhibitor, was an artifact (Specht et al. (1996) J. Biol. Chem. 271: 1943-49), the ensuing skepticism and confusion cast doubt on the existence of FABP isoforms in general. Yet, increasing data suggest that several FABPs, e.g. human intestinal I-FABP, bovine and mouse heart H-FABP, rabbit myelin P2 protein and bovine liver L-FABP may exist as true isoforms. In contrast, the rat liver L-FABP putative isoforms may actually be due either to bound ligand, post-translational S-thiolation and/or structural conformers. In any case, almost nothing is known regarding possible functions of either the true or putative isoforms in vitro or in vivo. The objective of this article is to critically evaluate which FABPs form biochemically defined or true isoforms versus FABPs that form additional forms, operationally defined as isoforms. In addition, recent developments in the molecular basis for FABP true isoform formation, the processes leading to additional operationally defined putative isoforms and insights into potential function(s) of this unusual aspect of FABP heterogeneity will be examined.

Animals↗
PubMed1998

Cellular differentiation and I-FABP protein expression modulate fatty acid uptake and diffusion.

The effect of cellular differentiation on fatty acid uptake and intracellular diffusion was examined in transfected pluripotent mouse embryonic stem (ES) cells stably expressing intestinal fatty acid binding protein (I-FABP). Control ES cells, whether differentiated or undifferentiated, did not express I-FABP. The initial rate and maximal uptake of the fluorescent fatty acid, 12-(N-methyl)-N-[(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-octadec anoic acid (NBD-stearic acid), was measured in single cells by kinetic digital fluorescence imaging. I-FABP expression in undifferentiated ES cells increased the initial rate and maximal uptake of NBD-stearic acid 1.7- and 1.6-fold, respectively, as well as increased its effective intracellular diffusion constant (Deff) 1.8-fold as measured by the fluorescence recovery after photobleaching technique. In contrast, ES cell differentiation decreased I-FABP expression up to 3-fold and decreased the NBD-stearic acid initial rate of uptake, maximal uptake, and Deff by 10-, 4.7-, and 2-fold, respectively. There were no significant differences in these parameters between the differentiated control and differentiated I-FABP-expressing ES cell lines. In summary, differentiation and expression of I-FABP oppositely modulated NBD-stearic acid uptake parameters and intracellular diffusion in ES cells.

4-Chloro-7-nitrobenzofurazan↗
PubMed1997

Isoforms of rat liver fatty acid binding protein differ in structure and affinity for fatty acids and fatty acyl CoAs.

Although native rat liver fatty acid binding protein (L-FABP) is composed of isoforms differing in isoelectric point, their comparative structure and function are unknown. These properties of apo- and holo-L-FABP isoforms were resolved by circular dichroism, time-resolved fluorescence spectroscopy, and binding/displacement of fluorescent ligands. Both apo-isoforms had similar hydrodynamic radii of 18.5 A, but apo-isoform I had a greater alpha-helical content and exhibited a longer Tyr lifetime, indicative of secondary and tertiary structural differences from isoform II. Isoforms I and II both had two fatty acid or fatty acyl CoA binding sites. Ligand binding decreased the isoform hydrodynamic radii by 3-4 A and increased Tyr rotational motions in a more restricted range. Fatty acyl CoAs were more effective than fatty acids in altering the isoform structures. Scatchard analysis showed that both isoforms bound cis- parinaric acid with high affinity (Kd values 41 and 60 nM, respectively) and bound trans-parinaric acid with 2- and 7-fold, respectively, higher affinity than for cis-parinaric acid. In contrast, isoform I had higher affinity for cis- and trans-parinaroyl CoAs (Kd values of 33 and 14 nM) than did isoform II (Kd values of 110 and 97 nM), thereby resulting in biphasic plots of parinaroyl-CoA binding to native L-FABP. Finally, displacement studies indicated that each isoform displayed distinct specificities for fatty acid/fatty acyl CoA chain length and unsaturation. Thus, rat L-FABP isoforms differ markedly in both structure and ligand binding function.

Acyl Coenzyme A↗
PubMed1997

The sterol carrier protein-2 fatty acid binding site: an NMR, circular dichroic, and fluorescence spectroscopic determination.

The interaction and orientation of fatty acids with recombinant human sterol carrier protein-2 (SCP-2) were examined by nuclear magnetic resonance (NMR), circular dichroism (CD), and fluorescence techniques. 13C-NMR spectroscopy of stearic acid and oleic acid as well as fluorescence spectroscopy of cis-parinaric acid demonstrated that SCP-2 bound naturally occurring fatty acids with near 1:1 stoichiometry. Several findings indicated that the fatty acid was oriented in the binding site with its methyl end buried in the protein interior and its carboxylate exposed at the surface: the chemical shift of bound [18-13C]-stearate; dicarboxylic/monocarboxylic acid cis-parinaric acid displacement; complete ionization of the carboxylate group of SCP-2 bound [1-13C]stearate at neutral pH; lack of electrostatic interactions between 13C-fatty acids with SCP-2 cationic residues: pH titratability of the SCP-2 bound [1-13C]stearate carboxylate group. SCP-2 did not undergo global structural changes upon ligand binding or pH decrease as indicated by the absence of significant changes in NMR and only small alterations in time resolved fluorescence parameters. However, SCP-2 did undergo secondary structural changes detected by CD in the pH range 5-6. While these changes in secondary structure did not alter the fatty acid:SCP-2 binding stoichiometry, the affinity for fatty acid was increased severalfold at lower pH. In summary, 13C-NMR, CD, and fluorescence spectroscopy provided a detailed understanding of the interaction of fatty acids with SCP-2 and further showed for the first time the orientation of the fatty acid within the binding site. The pH-induced changes in SCP-2 secondary structure and ligand binding activity may be important to the mechanism whereby this protein interacts with membrane surfaces to enhance lipid binding/transfer.

Binding Sites↗
PubMed1997

Time-resolved fluorescence of intestinal and liver fatty acid binding proteins: role of fatty acyl CoA and fatty acid.

The effect of fatty acyl CoA and fatty acid on the solution structure and dynamics of two intestinal enterocyte fatty acid binding proteins, intestinal (I-FABP) and liver (L-FABP), was examined by time-resolved fluorescence of FABP aromatic amino acid residues. I-FABP Trp displayed two rotational correlation times, 6.6 and 0.4 ns. reflecting motion of the protein as a whole and segmental mobility of Trp. Neither oleoyl CoA, oleic acid, nor CoASH altered overall I-FABP rotational correlation time. However, oleic acid and CoASH increased I-FABP Trp segmental mobility, while oleoyl CoA and CoASH decreased I-FABP Trp limiting anisotropy (order). The angle of I-FABP Trp "wobbling in a cone" was increased by ligands in the order oleoyl CoA > CoASH > oleic acid. L-FABP Trp segmental mobility. L-FABP overall rotational motion, in contrast to that of I-FABP, was significantly increased by ligands in the order oleoyl CoA > oleic acid > CoASH. cis-Parinaric acid and cis-parinaroyl CoA bound to L-FABP also reflected overall L-FABP motion but yielded longer rotational correlation times, 8.2 and 10.7 ns, than the respective apo-FABPs. Such effects were not observed with I-FABP. Finally, both cis-parinaric acid and cis-parinaroyl CoA were much less ordered in the I-FABP ligand binding site than with L-FABP. These observations suggest that the rotational dynamics of L-FABP and its conformation are more sensitive to ligands than I-FABP. Further, ligands such as fatty acids, fatty acyl CoAs, and/or CoASH differentially modulate the I-FABP and L-FABP dynamics, and the ligand binding sites of these proteins differ in their ability to order the ligands.

Acyl Coenzyme A↗
PubMed1997

Lipid specificity and location of the sterol carrier protein-2 fatty acid-binding site: a fluorescence displacement and energy transfer study.

Although it was recently recognized that sterol carrier protein-2 (SCP-2) interacts with fatty acids, little is known regarding the specificity of SCP-2 for long-chain fatty acids or branched-chain fatty-acid-like molecules. Likewise the location of the fatty-acid binding site within SCP-2 is unresolved. A fluorescent cis-parinaric acid displacement assay was used to show that SCP-2 optimally interacted with 14-22 carbon chain lipidic molecules: polyunsaturated fatty acids > monounsaturated, saturated > branched-chain isoprenoids > branched-chain phytol-derived fatty acids. In contrast, the other major fatty-acid binding protein in liver, fatty-acid binding protein (L-FABP), displayed a much narrower carbon chain preference in general: polyunsaturated fatty acids > branched-chain phytol-derived fatty acids > 14- and 16-carbon saturated > branched-chain isoprenoids. However, both SCP-2 and L-FABP displayed a very similar unsaturated fatty-acid specificity profile. The presence and location of the SCP-2 lipid binding site were investigated by fluorescence energy transfer. The distance between the SCP-2 Trp50 and bound cis-parinaric acid was determined to be 40 A. Thus, the SCP-2 fatty-acid binding site appeared to be located on the opposite side of the SCP-2 Trp50. These findings not only contribute to our understanding of the SCP-2 ligand binding site but also provide evidence suggesting a potential role for SCP-2 and/or L-FABP in metabolism of branched-chain fatty acids and isoprenoids.

Animals↗
PubMed1996

Sterol carrier protein-2, a new fatty acyl coenzyme A-binding protein.

The ability of sterol carrier protein-2 (SCP-2) to interact with long chain fatty acyl-CoAs was examined. SCP-2 bound fluorescent fatty acyl-CoAs at a single site with high affinity. Kd values for cis- and trans-parinaroyl-CoA were 4.5 and 2.8 nM, respectively. Saturated 10-18-carbon and unsaturated 14-20-carbon fatty acyl-CoAs displaced SCP-2-bound fluorescent ligand. Oleoyl-CoA and oleic acid (but not coenzyme A) significantly altered SCP-2 Trp50 emission and anisotropy decay, thereby increasing SCP-2 rotational correlation time, SCP-2 hydrodynamic radius, and SCP-2 Trp50 remaining anisotropy up to 1.7-, 1.2-, and 1.3-fold, respectively. These changes were not accompanied by significant alterations in protein secondary structure as determined by circular dichroism. Finally, SCP-2 differentially altered the fluorescence emission and anisotropy decays of bound cis- and trans-parinaroyl-CoA. Both fluorescent fatty acyl-CoAs were located within a very ordered (limited cone angle of rotation) environment within SCP-2, as shown by a remaining anisotropy of 0.365 and 0.361 and a wobbling cone angle of 12 and 13 degrees , respectively. These anisotropy values were very close to those of such ligands in a propylene glass. However, the rotational relaxation times exhibited by SCP-2-bound cis- and trans-parinaroyl-CoA, 8.4-8.8 ns, were longer than those for the corresponding free fatty acid, 7.5-6.6 ns. These data show for the first time that SCP-2 is a fatty acyl-CoA-binding protein.

Acyl Coenzyme A↗
PubMed1996

Fluorescence studies of lipid association-induced conformational adaptations of an exchangeable amphipathic apolipoprotein.

The conformational adaptability of Manduca sexta apolipophorin III (apoLp-III) has been evaluated by monitoring the spectroscopic properties of its sole tyrosine residue, Tyr145, present in the fifth helical segment of the protein. M. sexta apoLp-III adopts a globular five-helix bundle structure in solution and has been postulated to undergo an opening at putative hinge domains upon interaction with lipid surfaces. Previous results have shown that the intrinsic fluorescence of Tyr145 is highly quenched in the closed, water-soluble conformation but is dramatically enhanced upon lipid association. We have carried out a spectroscopic characterization of Tyr145 and its microenvironment, to enable its use as a structural probe of lipid-induced conformational changes of apoLp-III. The pKa of Tyr145 in lipid-free apoLp-III was found to be 10.5, as determined from uv-spectrophotometry, indicating that, in the ground state, the tyrosyl phenolic group is not ionized under physiological conditions. Compared to free tyrosine in aqueous buffer (pH 7.0), a red shift (77 nm) in the (lambda)max of absorbance of Tyr145 was observed, suggesting that an H-bonding interaction is responsible for the quenched state of tyrosine fluorescence. In an effort to explain the observed quenching phenomenon, the quantum yield and lifetimes of Tyr145 fluorescence emission were investigated as a function of pH and lipid binding. The quantum yield of Tyr145 in lipid-free apoLp-III was enhanced fivefold upon decreasing the pH, with a half-maximal point around pH 5.5. Time-resolved fluorescence decay analysis showed that Tyr145 exhibits nonexponential emission decay with two components having lifetimes of 3.3 ns (76%) and 0.89 ns (24%) in the lipid-free state. The lifetime and amplitude of Tyr145 remain essentially unaltered upon lipid association or decreasing the pH. This is consistent with the hypothesis that, in the lipid-free helix bundle conformation, a quenching residue exists within H-bonding distance of the phenolic side chain of Tyr145 which, at physiological pH, is responsible for the observed fluorescence quenching. Opening of the helix bundle repositions this acceptor base, possibly a carboxylate or an imidazole side chain, making it unavailable for quenching. Using differential polarized phase and modulation fluorometry, it was seen that the segmental motion of Tyr145 is also altered considerably upon lipid interaction. These spectroscopic and motional properties of Tyr145 distinguish this unique residue as a useful probe to monitor structural flexibility of apoLp-III.

Animals↗
PubMed1996

Spontaneous and protein-mediated sterol transfer between intracellular membranes.

Relatively little is known regarding intracellular cholesterol trafficking pathways. To resolve some of these potential pathways, spontaneous and protein-mediated sterol transfer was examined between different donor-acceptor membrane pairs in vitro using L-cell fibroblast plasma membrane (PM) and microsomal (MICRO) and mitochondrial (MITO) membranes. Several new exciting insights were provided. First, the initial rate of spontaneous molecular sterol transfer was more dependent on the type of acceptor than donor membrane, i.e. spontaneous intracellular sterol trafficking was vectorial. Therefore, the rate of sterol desorption from the donor membrane was not necessarily the rate-limiting step in molecular sterol transfer. Second, the rate of molecular sterol transfer was not obligatorily correlated with the direction of the cholesterol gradient. For example, although PM had a 3.2-fold higher cholesterol/phospholipid ratio than MITO, spontaneous sterol transfer was 4-5-fold faster up (MITO to PM) rather than down (PM to MITO) the concentration gradient. Third, sterol carrier protein-2 differentially stimulated the initial rate of sterol transfer for all donor-acceptor combinations, being most effective with PM donors: PM-MICRO, 27-fold; and PM-MITO, 12-fold. Sterol carrier protein-2 was less effective in enhancing sterol transfer in the reverse direction, i.e. MICRO-PM and MITO-PM (5- and 4-fold, respectively). Fourth, liver fatty acid-binding protein was limited in stimulating the initial rate of sterol transfer from PM to PM (1.5-fold), from PM to MITO (3-fold), and from MICRO to MITO (3-fold). In summary, these observations present important insights into potential sterol trafficking pathways between the major membrane components of the cell.

Animals↗
PubMed1996

Fibroblast membrane sterol kinetic domains: modulation by sterol carrier protein-2 and liver fatty acid binding protein.

The mechanism(s) of intracellular sterol trafficking among subcellular organelle membranes is not well understood. Relative contributions of vesicular, sterol carrier protein, and membrane sterol domain pathways are not resolved. A sterol kinetic assay was used to resolve multiple sterol domains in microsome (MICRO), mitochondria (MITO), and plasma (PM) membrane: exchangeable, 20-40% of total; non-exchangeable, 60-80% of total. Spontaneous sterol transfer between dissimilar donor and acceptor membranes was vectorial and depended both on acceptor and donor membrane properties. For example, sterol transfer from PM to MICRO or to MITO, or from MICRO to MITO was 3- to 5-fold slower as compared to sterol movement in the opposite direction. Sterol carrier protein-2 (SCP-2) stimulated sterol transfer in most donor/acceptor membrane combinations by decreasing exchange half-time but not domain size. SCP-2 enhanced sterol transfer selectively: PM-MICRO (12-fold); MITO-MITO, MICRO-MICRO, MICRO-PM (3-fold); PM-PM (1.4-fold); PM-MITO, MICRO-MITO (no effect). Thus, SCP-2-mediated sterol movement was vectorial and not necessarily down a membrane sterol concentration gradient. In contrast, liver fatty acid binding protein (L-FABP) revealed a modest (2-fold) stimulatory effect on sterol transfer only between PM-MITO and MICRO-MICRO. In conclusion, in vitro studies of sterol transfer among isolated subcellular membranes provided kinetic evidence for sterol domains in microsomes and mitochondria as well as plasma membranes. Furthermore, both spontaneous and protein-mediated sterol transfer appeared vectorial and selective in nature.

Animals↗
PubMed1994

Membrane ionic current photomodification by rose bengal and menadione: role of singlet oxygen.

Photosensitized modification of ionic leak current and potassium current was studied in frog cardiac atrial cells using whole cell patch clamp techniques. Rose bengal (RB) and menadione (MQ) were used as photosensitizers. Separate photophysical studies of the photosensitizers in deuterium oxide solution demonstrated that MQ did not produce singlet oxygen as evidenced by the lack of luminescence at 1270 nm, whereas RB was an efficient singlet oxygen generator. Both photosensitizers sensitized block of potassium current in atrial cells, and both sensitized an increase of ionic leak current. However, when photosensitizer concentrations and illumination intensities were adjusted to match the rate of block of potassium current by the two photosensitizers, there were dramatic differences in leak current increase, both quantitatively and qualitatively. Menadione sensitized a much slower increase in leak current than did RB. Further, the leak current sensitized by MQ had a more positive reversal potential than that sensitized by RB, suggesting a less potassium-selective leak current pathway. The results suggest that, while the effects of singlet oxygen and non-singlet oxygen modification of cell membranes may be similar, there may also be significant differences in the resulting membrane permeabilities. The results also demonstrate that MQ and RB may be useful agents to study the role of singlet oxygen versus non-singlet oxygen modification of biological systems.

Animals↗
PubMed1982

[Vertical displacements of the center of gravity in the cat during movement of limb flexion induced by motor cortex stimulation].

A limb movement and the corresponding postural adjustment results in a displacement of the body's center of gravity. The vertical component of this displacement has been calculated by measuring the variations of the sum of vertical forces at each limb. The displacements are upwards and are larger in the case of hindlimb flexion than forelimb flexion. Their amplitude is directly linked to the time course of the vertical force variations recorded at each limb. The feed-forward character of the postural adjustment appears to minimize this amplitude and this may allow us to discuss the functional significance of this postural adjustment.

Animals↗