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91.
The phase behavior of isolated photoreceptor membrane lipids is further investigated by 31P-NMR, in view of earlier discrepant results [(1979) Biochim. Biophys. Acta 558, 330–337; (1982) FEBS Lett. 124, 93–99]. We present evidence that the discrepancy is due to bivalent cations. When resuspended in aqueous media at neutral pH in the absence of bivalent cations, the isolated photoreceptor membrane lipids largely adopt the bilayer configuration. However, upon addition of such cations (Ca2+ Mg2+) or when resuspended in their presence, the formation of other phases (hexagonal HII, lipidic particles) results. The rate of this transition depends on cation concentration and temperature. The transition is not easily reversed by addition of EDTA. Implications with regard to photoreceptor membrane structure and function need further study. 相似文献
92.
Y. Kowyama T. Kawase H. Yamagata 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1984,68(4):297-303
Summary In order to examine changes in survival and mutation rates during a cell cycle in higher plant, fertilized egg cells of rice were irradiated with X-rays at 2 h intervals for the first 36 h after pollination, i.e., at different phases of the first and second cell cycles. The most sensitive phase in lethality was late G1 to early S, followed by late G2 to M, which were more sensitive than the other phases. In both M1 and M2 generations, sterile plants appeared most frequently when fertilized egg cells were irradiated at G2 and M phases. Different kinds of mutated characters gave rise to the respective maximum mutation rates at different phases of a cell cycle: namely, albino and viridis were efficiently induced at early G1, xantha at early S, short-culm mutant at mid G2, heading-date mutant at M to early G1. The present study suggests the possibility that the differential mutation spectrums concerning agronomic traits are obtained by selecting the time of irradiation after pollination. 相似文献
93.
Radioimmunoassay of neuropeptide Y 总被引:5,自引:0,他引:5
The development of a radioimmunoassay to the newly isolated peptide, neuropeptide Y is described. Four separate antisera have been developed using different immunisation schedules. Two of these antisera (YNI and YNIO) are directed to the C-terminal region of the peptide and cross-react with the related peptide PYY, whereas YN7 is specific being directed to the N-terminal region of NPY, YN6 is similarly specific for NPY, but is unable to bind the available fragments. These four antisera provide similar results for determination of NPY immunoreactivity within porcine brain extracts, however YN6 consistently undervalues all extracts from the other species examined (human, rat, guinea pig, cat and mouse). Chromatographic analysis by means of reverse phase high pressure liquid chromatography (HPLC) shows that NPY immunoreactivity of human extracts elutes in an earlier position than the porcine standard. It seems likely therefore that human and porcine NPY differ in their amino acid sequences. 相似文献
94.
Craig A. Halverson Alfred F. Esser Kenneth A. Souza 《Journal of cellular biochemistry》1978,8(2):129-138
Bacillus stearothermophilus cells vary the lipid fatty acid composition of cytoplasmic membranes with growth temperature. Spin label studies of such membranes have been interpreted to indicate lateral lipid phase separations at the growth temperature. We have now used freeze-fracture electron microscopy to confirm the spin label studies. Freeze-fracture faces of protoplasts indicate slight but distinct protein aggregation at the growth temperature. Aggregation increases rapidly with decreasing quench temperature in wild-type cells. In contrast we were unable to demonstrate extended protein segregation in membranes of a temperature-sensitive mutant that contains more than 58% branched fatty acids. Storage of protoplasts for prolonged times below the lipid phase transition results in the appearance of corrugated fracture faces with 300- to 500-Å repeat patterns, although this organism does not synthesize lecithins. 相似文献
95.
Angie Rizzino Alan B. Blumenthal 《In vitro cellular & developmental biology. Plant》1978,14(5):437-442
Summary We synchronized Drosophila cell lines (Schneider's line 2 and Kc) by allowing the cells to enter the stationary phase of growth and then diluting them into fresh culture medium. The cells
of both cell lines entered S phase, after an 8- to 14-hr delay, in a state of partial synchrony; 60 to 80% of the cell population
accumulated in S phase. Measurements of the cell cycle phases of Schneider's line 2 cells (S=14 to 16 hr; G2=6 to 8 hr; M=0.4 hr) were similar to those of Kc cells.
This work was performed under the auspices of the U.S. Energy Research and Development Administration. A.R. was supported
by an NIH post-doctoral fellowship, No. CA01060. 相似文献
96.
- 1. 1. The 31P-NMR characteristics of intact rat liver mitochondria, mitoplasts and isolated inner mitochondrial membranes, as well as mitochondrial phosphatidylethanolamine and phosphatidylcholine, have been examined.
- 2. 2. Rat liver mitochondrial phosphatidylethanolamine hydrated in excess aqueous buffer undergoes a bilayer-to-hexagonal (HII) polymorphic phase transition as the temperature is increased through 10°C, and thus prefers the HII) arrangement at 37°C. Rat liver mitochondrial phosphatidylcholine, on the other hand, adopts the bilayer phase at 37°C.
- 3. 3. Total inner mitochondrial membrane lipids, dispersed in an excess of aqueous buffer, exhibit 31P-NMR spectra consistent with a bilayer arrangement for the majority of the endogeneous phospholipids; the remainder exhibit spectra consistent with structure allowing isotropic motional averaging. Addition of Ca2+ results in hexagonal (HII) phase formation for a portion of the phospholipids, as well as formation of ‘lipidic particles’ as detected by freeze-fracture techniques.
- 4. 4. Preparations of inner mitochondrial membrane at 4 and 37°C exhibit 31P-NMR spectra consistent with a bilayer arrangement of the large majority of the endogenous phospholipids which are detected. Approx. 10% of the signal intensity has characteristics indicating isotropic motional averaging processes. Addition of Ca2+ results in an increase in the size of this component, which can become the dominant spectral feature.
- 5. 5. Intact mitochondria, at 4°C, exhibit 31P-NMR spectra arising from both phospholipid and small water-soluble molecules (ADP, Pi, etc.). The phospholipid spectrum is characteristic of a bilayer arrangement. At 37°C the phospholipids again give spectra consistent with a bilayer; however, the labile nature of these systems is reflected by increased isotropic motion at longer (at least 30 min) incubation times.
- 6. 6. It is suggested that the uncoupling action of high Ca2+ concentrations on intact mitochondria may be related to a Ca2+-induced disruption of the integrity of the inner mitochondrial phospholipid bilayer. Further, the possibility that non-bilayer lipid structures such as inverted micelles occur in the inner mitochondrial membrane cannot be excluded.
Keywords: 31P-NMR; Inner mitochondrial membrane; Phosphatidylethanolamine; Ca2+; Hexagonal (HII) phase; Lipidic particle 相似文献
97.
P.C. Noordam A. Killian R.F.M. Oude Elferink J. de Gier 《Chemistry and physics of lipids》1982,31(2):191-204
Comparative studies on bilayer systems of saturated phosphatidylcholines and phosphatidylethanolamines revealed a maximum in ionic permeability in phosphatidylcholine bilayers at the temperature of the gel to liquid-crystalline phase transition but such an increase in permeability was not detectable in bilayers of phosphatidylethanolamine. Furthermore, it was found that at the phase transition temperature the phosphatidylcholine bilayers are subject to rapid hydrolysis by pancreatic phospholipase A2 whereas phosphatidylethanolamine bilayers are not. These differences are discussed in view of detailed information on the molecular organization in the gel and liquid crystalline phases of the two phospholipid classes. 相似文献
98.
Imre Mezö János Seprödi Judit Érchegyi István Teplán Magdolna Kovacs Bela Flerkó 《Peptides》1983,4(2):149-151
Inhibitory analogues of luteinizing hormone-releasing hormone (LH-RH) were prepared with formyl-D-Trp1, acetyl-D-Trp1, valeryl-D-Trp1, tartaryl-D-Trp1, diacetyl-tartaryl-D-Trp1, acetyl-Gly1, and acetyl-Sar1 successively replacing the position one in the analogue [D-Trp1, D-p-Cl-Phe2, D-Trp3, D-Phe6, D-Ala10]-LH-RH. The formyl-D-Trp1 and acetyl-D-Trp1 analogues yielded 100% blockade of ovulation at the 10 μg dose; the others were less potent and inhibited ovulation at the 50 μg dose. The inhibitory potency seems to correlate with the polarity of the acyl group. 相似文献
99.
Tunicamycin, an inhibitor of the asparagine-linked protein N-glycosylation, blocks the initiation of DNA synthesis in Swiss 3T3 cells stimulated by prostaglandin F2α alone or with insulin. This effect is exerted only when tunicamycin is added from 0 to 8 h after stimulation and it decreases the rate of entry into S phase. Blocking of labeled sugar incorporation to proteins occurs regardless of the time of PGF2α stimulation. In contrast tunicamicin does not inhibit protein synthesis. These results suggest that N-glycoprotein synthesis early during the prereplicative phase is an important event controlling the mitogenic action of PGF2α 相似文献
100.