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The (Ca2+ + Mg2+)-ATPase purified from rabbit muscle sarcoplasmic reticulum has been reconstituted into a series of phosphatidylcholines in the liquid crystalline phase. For phosphatidylcholines containing monounsaturated fatty acyl chains, optimal activity is observed for a chain length of C18, with longer or shorter chains supporting lower activities. Phospholipids with methyl-branched chain saturated fatty acids support somewhat lower activities than the corresponding phospholipids with mono-unsaturated fatty acids. Mixed chain phospholipids support ATPase activities comparable to those shown by an unmixed chain phospholipid with the same average chain length. However, the response of the ATPase reconstituted with mixed chain phospholipids to the addition of oleyl alcohol is dominated by the longest fatty acyl chain. Based on their ability to displace brominated phospholipids, relative binding constants to the ATPase of a series of phosphatidylcholines have been determined. Binding to the ATPase is virtually unaffected by fatty acyl chain length or the presence of methyl branches. 相似文献
104.
Structural Characteristics and Nucleotide Sequence Analysis of Genomic RNA from RD-114 Virus and Feline RNA Tumor Viruses 总被引:5,自引:5,他引:0 下载免费PDF全文
James L. East John E. Knesek Patton T. Allen Leon Dmochowski 《Journal of virology》1973,12(5):1085-1091
The results of molecular hybridization experiments have demonstrated that the RNA genome of RD-114 virus has extensive nucleotide sequence homology with the RNA genome of Crandell virus, an endogenous type C virus of cats, but only limited homology with the RNA genomes of feline sarcoma virus and feline leukemia virus. The genomic RNAs of RD-114 virus and Crandell virus also had identical sedimentation coefficients of 50S. A structural rearrangement of genomic RNA did not exist within released RD-114 virions, whereas a structural rearrangement of genomic RNA did occur within feline sarcoma virions and feline leukemia virions after release from virus-producing cells. 相似文献
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Phospholipase A2 was isolated from human sperm and its potential role in the membrane fusion events of fertilization was examined. Highly purified enzyme hydrolyzed the phospholipids of [1-14C]oleate-labeled Escherichia coli optimally at neutral to alkaline pH with 5 mM CaCl2 and 150 mM NaCl (specific activity = 20 mumol/min/mg). Activity was inhibited in a dose-dependent manner by an oligomer of prostaglandin B1 (IC50 = 1.5 microM) reported to inhibit human phospholipases A2 in vitro and in situ. Sperm phospholipase A2 injected into mouse foot pad induced a dose-dependent edema that was inhibited by oral administration of prostaglandin Bx (IC50 < or = 10 mg/kg) or by pretreatment of the enzyme with 4-bromophenacyl bromide. Human sperm phospholipase A2 (10 micrograms) induced fusion of phosphatidylserine vesicles in the presence of 1 mM calcium chloride by approximately 80% (+/- 10%) as determined by monitoring turbidity (O.D.400) and efficiency of fluorescence resonance energy transfer. This enzyme-induced fusion was accompanied by phospholipid hydrolysis, and both fusion and phospholipid degradation were inhibited by more than 60% when enzyme was preincubated with 5 microM prostaglandin Bx. Sperm penetration of zona pellucida-free hamster oocytes was inhibited in a dose-dependent fashion when sperm were incubated with prostaglandin Bx (IC50 approximately 15 microM) during capacitation; sperm motility was not affected by this treatment. Capacitation in the presence of prostaglandin Bx had little to no effect on the in vitro acrosome reaction. These results suggest that sperm phospholipase A2 and its modulators may contribute to membrane fusion events in mammalian fertilization. 相似文献
108.
A survey was made of the yeast communities isolated from necrotic tissue of 4 species of prickly-pear cacti (Opuntia stricta, O. tomentosa, O. monacantha, andO. streptacantha) which have colonized in Australia. Yeast communities were sampled from a number of localities and at different times. Cactus specific yeasts accounted for 80% of the total isolates, and the 3 most common species contributed 63% of the total. Comparisons of the species compositions of the yeast communities indicated that the differences among communities were greater betweenOpuntia species than between different localities within a single cactus species, and also that differences between years were greater than average differences between localities within years. Multivariate statistical tests of association between yeast community and physical features of rots indicated that temperature, pH, and age of rot all exerted some influence on the structure of the yeast community. Similar analyses involvingDrosophila species inhabiting these cactus rots suggested the existence of complex associations betweenDrosophila community, yeast community, and physical and chemical attributes of the cactus necroses. 相似文献
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Monoclonal antibodies to the major protein of the murine zona pellucida: effects on fertilization and early development 总被引:2,自引:0,他引:2
The growing murine oocyte is surrounded by an extracellular zona pellucida consisting of three sulfated glycoproteins, ZP-1, ZP-2, and ZP-3. The smallest of these, ZP-3, has been reported to be the species-specific sperm receptor. Monoclonal antibodies have been recently characterized to three different antigenic determinants, two found exclusively on ZP-2, and one found on both ZP-2 and ZP-3. The in vivo effect of these antibodies on the three known functions of the zona pellucida were examined. The most dramatic effect was the prevention of fertilization. After administration, the monoclonal antibodies were located in the ovary on the zona pellucida of growing oocytes. Eggs ovulated subsequently were coated with the monoclonal antibodies and failed to develop into 2-cell embryos after mating. Eighty days later, the monoclonal antibodies could no longer be detected on the zona of ovarian oocytes, and this loss coincided with the resumption of fertility. These findings provide molecular evidence for the hypothesis that the immunological block to sperm-egg binding need not involve antibody specific for the sperm receptor, and that antibodies to the zona pellucida block sperm access by steric hinderance. Other known functions of the zona were unaffected. The antibodies were unable to induce the biochemical changes in the zona associated with the postfertilization block to polyspermy and had no detectable effect on preimplantation development. 相似文献
110.
A kinetic model for Ca2+ efflux mediated by the Ca2+ + Mg2+-activated ATPase of sarcoplasmic reticulum. 下载免费PDF全文
We present a model for Ca2+ efflux from vesicles of sarcoplasmic reticulum (SR). It is proposed that efflux is mediated by the Ca2+ + Mg2+-activated ATPase that is responsible for Ca2+ uptake in this system. In the normal ATPase cycle of the ATPase, phosphorylation of the ATPase is followed by a conformational change in which the Ca2+-binding sites change from being outward-facing and of high affinity to being inward-facing and of low affinity. To mediate Ca2+ efflux, it is proposed that the ATPase can adopt a conformation in which the Ca2+-binding sites are of low affinity but still outward-facing. It is shown that experimental data on the rates of Ca2+ efflux can be simulated in terms of this model, with Ca2+-binding-site affinities previously proposed to explain ATPase activity [Gould, East, Froud, McWhirter, Stefanova & Lee (1986) Biochem. J. 237, 217-227]. Effects of Mg2+ and adenine nucleotides on efflux rates are explained. It is suggested that Ca2+ efflux from SR mediated by the ATPase could be important in excitation-contraction coupling in skeletal muscle. 相似文献