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S Lefebvre

Publications and source records attributed to S Lefebvre.

59 records · Page 4Linked to original sources
PubMed1987

Calcium binding to untreated and dephosphorylated porcine neurofilaments.

The calcium-binding properties of untreated and in vitro dephosphorylated neurofilaments were determined by partition centrifugation. Scatchard plot analysis of the binding data indicated that each type of neurofilament contained both high and low affinity calcium-binding sites. The number of calcium-binding sites per unit consisting of three 140,000, three 107,000 and eight 62,000 molecular weight subunits was 4 sites with Kd = 4.1 microM and 126 sites with Kd = 293 microM for untreated neurofilaments. The in vitro dephosphorylated neurofilaments contained 8 sites with Kd = 15 microM and 54 sites with Kd = 332 microM, per unit.

Alkaline Phosphatase↗
PubMed1986

Dephosphorylation of neurofilaments by exogenous phosphatases has no effect on reassembly of subunits.

Exhaustive in vitro dephosphorylation of porcine neurofilaments (NFs) by alkaline or acid phosphatase did not cause a dissociation of the 210-kD (NF-H), 160-kD (NF-M), or 70-kD (NF-L) subunits and had no effect on the reassembly of NFs from urea or guanidine solution. Electron microscopy revealed that the NFs reassembled from isolated or dephosphorylated subunits had similar morphologies. Phosphatase treatment caused significant increases in the mobilities of NF-M and NF-H on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, suggesting that the subunits underwent marked conformational changes after dephosphorylation. Chemical phosphate analysis showed that as isolated NF-H, NF-M, and NF-L contained about 22, 11, and 3 mol phosphate/mol polypeptide, respectively. The corresponding values for the three subunits from alkaline phosphatase-treated NFs were about 8, 6, and 2 mol phosphate/mol polypeptide, respectively. These results indicate the occurrence of a class of phosphate moieties that is not accessible to exogenous phosphatases.

Acid Phosphatase↗
PubMed1984

Oxido-reduction of B800-850 and B880 holochromes isolated from three species of photosynthetic bacteria as studied by electron-paramagnetic resonance and optical spectroscopy.

Certain redox properties of bacteriochlorophyll alpha were used to probe the structure of several light-harvesting pigment-protein complexes or holochromes. To attribute redox properties unequivocally to a given holochrome, we worked with purified holochromes. We developed purification procedures for the B880 holochromes from Rhodospirillum rubrum, Rhodopseudomonas sphaeroides and Ectothiorhodospira sp. and for the B800-850 holochromes from the latter two species. In all these holochromes, bacteriochlorophyll alpha could be oxidized by ferricyanide as witnessed by the bleaching of their near-infrared absorption bands. However, only in B880 holochromes was this oxidation reversible. Another important difference between the B800-850 and the B880 holochromes is that oxidation of the latter gives rise to a g = 2.0025 electron paramagnetic resonance (EPR) signal with linewidth varying, according to species, from 0.37 mT to 0.48 mT. Both the reversible EPR signal and absorption changes titrate with a midpoint redox potential (pH 8.0) of approximately 570 mV. Linewidth narrowing can be interpreted by delocalization of the free electron spin over approximately 12 bacteriochlorophyll molecules. While the B880 holochromes from the three species considered had indistinguishable redox properties, the B800-850 holochromes differed from one another by their circular dichroic spectra and by the relative ease of oxidation of their 800-nm and 850-nm bands. This indicates that, contrary to the B880 holochromes, the B800-850 holochromes may not form a homogeneous class.

Bacterial Proteins↗