Isolation and characterization of a basic encephalitogenic protein from the central nervous system of sheep.

A basic protein has been purified from sheep brain. The purified protein sedimented in the analytical centrifuge at 56,000 r.p.m. as an homogenous product. This protein induced an allergic encephalitis when injected into guinea pigs. Some physiochemical properties of the protein were studied: the sedimentation coefficient was 1.52 and the molecular weight was 20,000 +/- 2,000, as estimated by electrophoresis in acrylamide gels containing SDS and urea; the specific extinction coefficient (see article) was 6.01 +/- 0.20. The aminoacid composition of the molecule was determined and its most prominent aspects are a high content of arginine and lysine, the presence of a single tryptophan, the total absence of cysteine and cystine and a blocked N-terminal residue. All these properties are very close to those of human and bovine encephalitogenic proteins.     

Separation of mammalian cell surface proteins by a two-dimensional gel electrophoresis system

Separation of externally exposed plasma membrane proteins of mammalian cells has been achieved by a new two-dimensional gel electrophoresis system. The proteins were separated in the first dimension on cylindrical polyacrylamide gels containing 0.1% sodium dodecyl sulfate (SDS) and in the second dimension on polyacrylamide slab gels containing 9 M urea, 0.1% SDS, and 0.1% Triton CF10. Using this method we have obtained reproducible high-resolution patterns of cell surface proteins of differentiated rat neuro-tumor cells in culture and of normal rat retinal cells. Different cell types show characteristic cell surface proteins in addition to ubiquitous ones. The number of common surface proteins between two cell types account for approximately half of the total surface proteins. By immunoprecipitation we have also found that rabbit anti-serum against a rat neuronal cell line can recognize most of these external proteins. Since the separation in the first dimension is done in the presence of SDS and the second dimension in the presence of SDS, a non-ionic detergent, and urea, the technique is particularly suitable for proteins that are of poor solubility. In addition to size, net charge and hydrophobicity appear to be important factors in the separation. Virtually all of the proteins that run in the first dimension can be recovered and further separated in the second.     

Multiple subunits in human ferritins: Evidence for hybrid molecules

The subunit composition of human heart and liver ferritins was examined by both sodium dodecyl sulfate gel electrophoresis and acetic acidurea gel electrophoresis. These analyses indicated that both tissues contained two subunit types of similar size but different surface charge. One subunit was common to both tissues. The implications of these findings in relation to the known heterogeneity of isoferritins are discussed, and a new model of ferritin structure is proposed.     

The effects of deuterium oxide (2H2O) on the polymerization of tubulin in vitro

The initial rate and final extent of polymerization of both bovine brain tubulin and sea urchin egg tubulin were enhanced in the presence of ²H₂O. The yields were increased in association with the elevation of the ²H₂O concentration. ²H₂O also reduced the critical concentration for polymerization of brain tubulin. Thermodynamic analysis was attempted using the temperature dependence of the critical concentration for polymerization in the presence of ²H₂O. We obtained linear van 't Hoff plots and calculated thermodynamic parameters which were positive and were increased with the elevation of the ²H₂O concentration. The enhancement of the polymerization of tubulin by ²H₂O could, therefore, be the result of the strenghening of intra-and/or inter-molecular hydrophobic interactions of the tubulin molecules. We believe that the increase in lenghth and number of microtubules of the mitotic spindles in the dividing cells of the eukaryotes with ²H₂O may be caused by the direct involvement of ²H₂O in the polymerization of tubulin.     

Further characterization of the lipid-depleted bovine rhodopsin obtained by cholate-ammonium sulfate fractionation

The rhodopsin preparation obtained by the method of ammonium sulfate fractionation contained 3–6 mol phospholipid and about 18 mol cholate per mol rhodopsin. The purified rhodopsin had 74% helical structure and showed a visible CD spectrum different from that of rhodopsin in the membrane. The rhodopsin was stable below but denatured gradually above 20°C. The lifetime of metarhodopsin I was long in this preparation. Regeneration capacity was low and only 30% of the original rhodopsin was regenerable by addition of 11-cis-retinal after bleaching.50 mol of phosphatidylcholine were maximally bound to 1 mol rhodopsin when the purified rhodopsin was mixed with phosphatidylcholine in 0.5% cholate. The rhodopsin recombined with lipid had properties similar to those of the original rhodopsin in the membrane. Exchange of cholate for other detergents was easily performed by dialysis. The rhodopsin preparation in which cholate was exchanged for digitonin gave almost the same CD, thermal stability and regenerability as those of a native rhodopsin in the membrane but metarhodopsin I still retained its long lifetime.     

Photosensitized cross-linking of erythrocyte membrane proteins. Evidence against participation of amino groups in the reaction

Exposure of human erythrocyte ghosts (pH 8, 10°C) to visible light in the presence of the photosensitizer, methylene blue, results in a relatively rapid loss of spectrin (bands 1 and 2 on sodium dodecyl sulfate gel electropherograms) and the appearance of high molecular weight cross-linked derivatives. Isolated spectrin also undergoes photosensitized cross-linking, indicating that the reaction is not lipid-dependent.Extensive cross-linking was neither reversed by dithiothreitol nor prevented by prior blocking of SH groups with $\text{N-}\text{ethylmaleimide}$, suggesting that cysteine residues are not crucial bridging sites. The possible requirement for NH₂ groups, as suggested by previous model studies (Dubbelman, T.M.A.R., de Goeij, A.F.P.M. and van Steveninck, J. (1978) Biochim. Biophys. Acta 511, 141–151), was tested. Succinylation of spectrin protected against cross-linking, but this effect is attributed to the disruption of quaternary structure, as deduced from sedimentation measurements. However, virtually complete blocking of NH₂ groups by amidination perturbed overall structure relatively little, and had no effect on cross-linking. Moreover, exogenous amines such as ethylamine, added in large excess to spectrin prior to irradiation, did not interfere with cross-link formation. These results suggest that NH₂ groups are not involved in the reaction.     

昆虫击倒抗性基因突变对钠通道功能的影响

该文综述了昆虫钠通道基因的表达与功能特性、击倒抗性突变的功能和这些突变对钠通道门控的影响,以及钠通道基因突变与抗性表现型之间的因果关系;还讨论了这些突变增强击倒抗性的分子机理。