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71.
Some characteristics of guanylate cyclase (GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2) in subcellular fractions prepared from rat cerebellum have been analyzed on the basis of responsiveness to N-methyl-N'-nitro-N-nitrosoguanidine and inhibitors related to N-nitroso compounds. The enzyme in 100 000 X g supernatant and crude mitochondrial (P2) fractions were differently activated (11- and 2.5-fold, respectively) by N-methyl-N'-nitro-N-nitrosoguanidine. The soluble fraction obtained by hypo-osmotic treatment and subsequent recentrifugation of the P2 (P2-soluble) contained a significantly higher total guanylate cyclase activity than that of the starting material (P2). The P2-soluble fraction also exhibited a lower responsiveness (1.5-fold) to N-methyl-N'-nitro-N-nitrosoguanidine than that found in the P2. The membrane fraction prepared from the P2 (P2-membrane) had no response to N-methyl-N'-nitro-N-nitrosoguanidine. Hemoglobin and vitamin A derivatives significantly inhibited both N-methyl-N'-nitro-N-nitrosoguanidine-activated 100 000 X g supernatant and basal P2-soluble enzyme activities, without effect on the basal activities in 100 000 X g supernatant and P2-membrane fractions. The present results suggest that two different types of guanylate cyclase may be present in rat cerebellum in terms of the responsiveness of N-nitroso compounds, and P2-soluble guanylate cyclase seems to be activated endogenously through a mechanism similar to the action of N-methyl-N'-nitro-N-nitrosoguanidine. 相似文献
72.
Summary
Tra
+and tra
–derivatives of drug resistance plasmid, R100-1, were isolated by phage P1 from an Hfr donor with integrated R100-1 and then analyzed by complementation tests with tra
–point mutants of Flac. Tra
+derivatives of R100-1 carrying tetracycline resistance alone and those carrying all six drug-resistance genes could support transfer of tra
–point mutants of Flac except Flac traJ, whereas all of tra
–derivatives of R100-1 failed to complement any one of tra
–point mutants of Flac. This suggests that these tra
–derivatives of R100-1 carrying tetracycline resistance gene are deleted for all the transfer genes impaired in the Flac point mutants tested. We assume a hot point, probably a specific base sequence similar to an IS element, at the left of the tetracycline gene (Fig. 1) becomes a transduction terminus in transduction of the integrated R100-1 by phage P1. Complementation analysis of tra
–derivatives carrying five resistance genes except the tetracycline gene led us to a supposition that a gene(s), probably analogous to traJ of the F plasmid, is located on R100-1 near the tetracycline gene which plays an important regulatory role for self-transfer as well as for the complementation of tra
–Flac mutants. 相似文献
73.
74.
Masato Hirata Takafumi Hamachi Eiichi Suematsu Toshitaka Koga 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1983,763(4)
Effects of N-formyl chemotactic peptides on the Ca2+ influx and efflux were investigated in guinea-pig peritoneal macrophages using an isotope tracer. fMet-Leu-Phe did not enhance the influx of 45Ca2+ into macrophages, whereas it stimulated the efflux of 45Ca2+ from macrophages at concentrations ranging from 10−10 M to 10−7 M. fMet-Met-Met and fMet-Leu also stimulated the 45Ca2+ efflux, albeit at much higher concentrations, while there was no stimulation with fMet. The mitochondrial inhibitors, oligomycin and NaN3, did not modify the 45Ca2+ efflux induced by the chemoattractants, yet they did induce the release of 45Ca2+ from the mitochondria. On the other hand, higher concentrations of the calmodulin antagonists, chlorpromazine and trifluoperazine, induced the release of 45Ca2+ from the NaN3-insensitive Ca2+ store site and mimicked the enhancement of the 45Ca2+ efflux by N-formyl chemotactic peptides. Thus, N-formyl chemotactic peptides appear to increase the levels of intracellular free Ca2+ in guinea-pig peritoneal macrophages, probably by inducing the release of Ca2+ from the NaN3-insensitive Ca2+ store site. 相似文献
75.
Masato Hirata Takafumi Hamachi Eiichi Suematsu Toshitaka Koga 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1983,763(4):339-345
Effects of N-formyl chemotactic peptides on the Ca2+ influx and efflux were investigated in guinea-pig peritoneal macrophages using an isotope tracer. fMet-Leu-Phe did not enhance the influx of 45Ca2+ into macrophages, whereas it stimulated the efflux of 45Ca2+ from macrophages at concentrations ranging from 10?10 M to 10?7 M. fMet-Met-Met and fMet-Leu also stimulated the 45Ca2+ efflux, albeit at much higher concentrations, while there was no stimulation with fMet. The mitochondrial inhibitors, oligomycin and NaN3, did not modify the 45Ca2+ efflux induced by the chemoattractants, yet they did induce the release of 45Ca2+ from the mitochondria. On the other hand, higher concentrations of the calmodulin antagonists, chlorpromazine and trifluoperazine, induced the release of 45Ca2+ from the NaN3-insensitive Ca2+ store site and mimicked the enhancement of the 45Ca2+ efflux by N-formyl chemotactic peptides. Thus, N-formyl chemotactic peptides appear to increase the levels of intracellular free Ca2+ in guinea-pig peritoneal macrophages, probably by inducing the release of Ca2+ from the NaN3-insensitive Ca2+ store site. 相似文献
76.
The electron transfer from ubiquinol-2 to ferricytochrome c mediated by ubiquinol:cytochrome c oxidoreductase [E.C. 1.10.2.2] purified from beef heart mitochondria, which contained one equivalent of ubiquinone-10 (Q10), was investigated under initial steady-state conditions. The Q10-depleted enzyme was as active as the Q10-containing one. Double reciprocal plots for the initial steady-state rate versus one of the two substrates at various fixed levels of the other substrate gave parallel straight lines in the absence of any product. Intersecting straight lines were obtained in the presence of a constant level of one of the products, ferrocytochrome c. The other product, ubiquinone-2, did not show any significant effect on the enzymic reaction. Ferrocytochrome c non-competitively inhibited the enzymic reaction against either ubiquinol-2 or ferricytochrome c. These results indicate a Hexa-Uni ping-pong mechanism with one ubiquinol-2 and two ferricytochrome c molecules as the substrates, which involves the irreversible release of ubiquinone-2 as the first product and the irreversible isomerization between the release of the first ferrocytochrome c and the binding of the second ferricytochrome c. Considering the cyclic electron transfer reaction mechanism, this scheme suggests that the binding of quinone or quinol to the enzyme and electron transfer between the iron-sulfur center and cytochrome c1 are rigorously controlled by the electron distribution within the enzyme. 相似文献
77.
K Shinzawa-Itoh H Yamashita S Yoshikawa Y Fukumoto T Abe T Tsukihara 《Journal of molecular biology》1992,228(3):987-990
Fully reduced and CO-bound fully reduced forms of cytochrome c oxidase from beef heart muscle were crystallized in the presence of sodium ascorbate under N2 or CO atmosphere. Hexagonal bipyramidal and tetragonal crystals were obtained for both forms depending on buffer species. The hexagonal bipyramidal crystals, as large as 0.6 mm in the largest dimension, diffracted X-rays at 7 A resolution, showing an identical space group and cell dimension, P6(2) or P6(4) and a = b = 209 A, c = 283 A, respectively. These parameters coincide with those for crystals of the fully oxidized resting enzyme. This result suggests that a large conformational change, like a subunit arrangement, is not induced by the redox change and/or binding of CO (and possibly O2) to heme a3. 相似文献
78.
The complete nucleotide sequence of the phosphoprotein (P) gene of the Yamagata-1 strain of a defective subacute sclerosing panencephalitis (SSPE) virus was determined. Comparison with the P gene of the Edmonston strain of measles virus (MV) revealed 44 differences of which 23 nucleotides substitutions were identical with those revealed between other SSPE viruses and MV (Cattaneo et al. (1989) Virology 173, 415-425). The consensus sequence of the G insertion site was completely conserved, whereas mRNAs with one or three non-templated G residue insertions were found in addition to the mRNA of the exact genome copy. As a result of the frameshift downstream of the site of G insertion, the cysteine-rich V protein was predicted from the one G-inserted mRNA besides the P and C proteins predicted from the genome-copied mRNA. 相似文献
79.
S Tuzi K Shinzawa-Itoh T Erata A Naito S Yoshikawa H Sait? 《European journal of biochemistry》1992,208(3):713-720
We have recorded 100.6-MHz high-resolution solid-state 13C-NMR spectra of crystalline cytochrome-c oxidase from bovine heart muscle and hen egg-white lysozyme, to compare conformation and dynamics of a typical membrane-protein complex with those of lysozyme. The absence of severe interference with the solid-state 13C-NMR spectra, from both the line broadenings from paramagnetic centers and overlapping of intense detergent signals, provided spectral resolution of 13C-NMR feature of cytochrome-c oxidase crystals comparable to that of lysozyme crystal and better than that of dissolved or lyophilized samples. In fact, the observed peak intensities of the polar heads of the detergents BL8SY and Brij 35 were only about 10% and 3% of the anticipated values, respectively. The dynamic behavior of the backbone and side chains of cytochrome-c oxidase was compared with that of lysozyme on the basis of the 13C spin-lattice relaxation times (T1): the backbone of the cytochrome-c oxidase turned out to be more flexible than that of lysozyme. Molecular motions of the detergent molecules attached to the proteins are found to be highly heterogeneous. Detergent molecules undergo rapid tumbling motions in the crystals in about 10 ns as detected by T1. In addition to rapid motions, slow motions were detected by 1H spin-lattice relaxation time in the rotating frame (TH1 rho) and cross-polarization time (TCH), together with data from static spectra, indicating that the aliphatic portion of the detergent interacts more strongly with hydrophobic protein surfaces than do the polar heads. 相似文献
80.
To investigate the reactions involved in the biosynthesis of vindoline from tabersonine, the bioconversion products formed when the latter compound was fed to cell suspension cultures of Catharanthus roseus were isolated and characterized. Two biotransformation products of tabersonine were isolated and shown to be lochnericine, which is formed by epoxidation of tabersonine at positions 14, 15, and lochnerinine, the 11-methoxylation product of lochnericine. The bioconversion ratio of the main biotransformation product, lochnericine, reached a value of 80.6% within three days. 相似文献