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21.
Metabolism of 32-hydroxy-24,25-dihydrolanosterol (lanost-8-ene-3 beta,32-diol), a posturated intermediate of the 14 alpha-demethylation (removal of C-32) of 24,25-dihydrolanosterol (lanost-8-en-3 beta-ol), by a reconstituted system consisting of yeast cytochrome P-450 which catalyzes lanosterol 14 alpha-demethylation (cytochrome P-45014DM) (Yoshida, Y., and Aoyama, Y. (1984) J. Biol. Chem. 259, 1655-1660 and Aoyama, Y., Yoshida, Y., and Sato, R. (1984) J. Biol. Chem. 259, 1661-1666) and NADPH-cytochrome P-450 reductase was studied. The reconstituted system converted both 32-hydroxy-24,25-dihydrolanosterol and 24,25-dihydrolanosterol to 4,4-dimethyl-5 alpha-cholesta-8,14-dien-3 beta-ol, the 14 alpha-demethylated product of the latter. The metabolism of these compounds was inhibited by a low concentration of ketoconazole which is a potent cytochrome P-45014DM inhibitor. Affinity of cytochrome P-45014DM for 32-hydroxy-24,25-dihydrolanosterol was about 20 times higher than for 24,25-dihydrolanosterol and the cytochrome metabolized the former about 4 times faster than the latter under the experimental conditions. Spectral analysis suggested that the 32-hydroxyl group of 32-hydroxy-24,25-dihydrolanosterol interacted with the heme iron of the oxidized cytochrome and this interaction might support the high affinity of this compound for the cytochrome. These lines of evidence indicate that 32-hydroxy-24,25-dihydrolanosterol is the intermediate of the 14 alpha-demethylation of 24,25-dihydrolanosterol by cytochrome P-45014DM. It is also clear that the cytochrome catalyzes further metabolism of the 32-hydroxylated intermediate to the 14 alpha-demethylated product with higher efficiency than the 32-hydroxylation of the substrate. Cytochrome P-45014DM is thus classified as lanosterol C14-C32 lyase. 相似文献
22.
M Ogata S Sato H Sano T Hamaoka H Doi K Nakanishi Y Asano T Itoh H Fujiwara 《Journal of immunology (Baltimore, Md. : 1950)》1987,139(8):2675-2682
A recently established thymic stroma-derived cell line (TSCL) supported the growth of the interleukin (IL) 2-dependent, antigen-specific helper T cell (Th) clone, 9-16, without requirement for IL-2 and antigen, and such growth was substituted by a factor produced into cultures by this established TSCL. This substance, thymic stroma-derived T cell-growth factor (TSTGF), was capable of inducing the proliferation of various Th clones including 9-16 Th clone, but not of cytotoxic T cell clones. TSTGF-induced growth promotion was obtained in a dose-dependent fashion and in maintaining antigen specificity of Th clones. The culture supernatant from the TSCL did not contain detectable level of IL-1, IL-2, IL-3, IL-4, or interferon activity. The proliferation of 9-16 Th clone was stimulated by recombinant IL-2 and IL-4 as well as TSTGF, but not by IL-1, IL-3, or interferons. However, the proliferation of this Th clone by IL-2 or IL-4 was almost completely inhibited by anti-IL-2 receptor or anti-IL-4 monoclonal antibody, respectively, whereas TSTGF-induced growth of 9-16 Th clones was not affected by either type of antibody, demonstrating that TSTGF is functionally distinct from IL-2 and IL-4. In addition, TSTGF activity was also obtained from the culture supernatant of the primary thymic explant, which was freshly prepared. These results indicate that the primary thymic explant as well as an established TSCL produce factors capable of promoting the growth of helper but not cytotoxic type of T cells in the absence of T cell growth factors thus far defined. 相似文献
23.
Murine monoclonal antibodies to the myelin-associated glycoprotein (MAG) recognize Leu-7-reactive molecules on human mononuclear cells 总被引:2,自引:0,他引:2
M Arai M Nishizawa T Inuzuka M Tanaka H Baba S Sato T Miyatake 《Journal of immunology (Baltimore, Md. : 1950)》1987,138(10):3259-3263
It is known that the antibody to human myelin-associated glycoprotein (MAG) reacts with a subset of human mononuclear cells (MNC) mediating a natural killer (NK) activity. The properties of the target molecule of the anti-MAG antibody, however, have not yet been elucidated. Three (GC-J4, MC-P2, and MC-P4) of five murine monoclonal antibodies (mAb) to MAG bound to human MNC. Moreover, MC-P2 and MC-P4 inhibited the binding of 125I-labeled anti-Leu-7 to MNC in a dose-dependent fashion. Conversely, anti-Leu-7 inhibited the binding of MC-P2 and MC-P4 to MNC, but did not inhibit the binding of GC-J4. Therefore, it is possible that MC-P2 and MC-P4 bind directly to or close to the Leu-7 epitope, and that GC-J4 binds to the epitope which is distinct from the Leu-7 epitope. The electrophoretic patterns of immunoprecipitates with GC-J4, MC-P2 and anti-Leu-7 from detergent lysates of surface-labeled human MNC were very similar. The target molecules of anti-Leu-7 and anti-MAG mAb have apparent m.w. of 205, 170, 150, 135, 110, 85, 65, and 55 kDa. All of the molecules precipitated by these mAb are monomeric or noncovalently associated proteins, because the electrophoretic mobilities of the proteins remained unchanged whether the samples were reduced or not. MC-P4 may have a higher affinity for the 65 kDa molecule than the other mAb, and precipitates the 58 kDa molecule as well. Therefore, the fine antigenic specificity of MC-P4 is slightly different from those of anti-Leu-7 or MC-P2. The implication of these results is that mAb, whose specificity is directed to the carbohydrate part of human MAG, reacts with the Leu-7 reactive molecules on human MNC, and that at least two epitopes detected by anti-MAG mAb coexist on the surface molecules with various apparent m.w. 相似文献
24.
Optimum conditions for electric pulse-mediated gene transfer to mammalian cells in suspension 总被引:5,自引:0,他引:5
H Hama-Inaba M Takahashi M Kasai T Shiomi A Ito F Hanaoka K Sato 《Cell structure and function》1987,12(2):173-180
A pulse-generating machine which delivers exponentially decaying pulses over broad range of pulse lengths was used to determine the optimum pulse conditions for gene transfer to FM3A cells. In the transformation of tk- cells with pTK1, a single pulse of 100-2000 microseconds gave a high transformation frequency at 1.5-6 kV/cm and room temperature, the highest transformation frequency obtained being 3 X 10(-3). As the suspension buffer for cells exposed to the pulse, Saline G was better than PBS(-) for obtaining a large number of transformants because it ensured high cell viability. 相似文献
25.
In order to identify the intracellular transmitter involved in the taste transduction process, cyclic nucleotides were iontophoretically injected into the frog taste cells while membrane potentials were recorded intracellularly. Injection of either cyclic GMP or cyclic AMP induced a depolarization response of about 5 mV in the taste cells, but injection of Cl- had no effect. The rate of a repolarization after the depolarization elicited by cyclic GMP was larger than that after cyclic AMP. The possible role of cyclic nucleotide in the taste transduction was discussed. 相似文献
26.
N-Ethylmaleimide dose dependently inhibited platelet aggregation induced by collagen or arachidonate but did not inhibit the aggregation by thrombin or ionophore A23187 within the concentrations tested. [3H]Arachidonate release from membrane phospholipids of the collagen-stimulated platelets was inhibited by N-ethylmaleimide in parallel with the inhibition of aggregation, but not in response to A23187. N-Ethylmaleimide prevented 45Ca2+ influx into platelet cells from outer medium induced by collagen, and also inhibited the increase in the concentration of cytoplasmic free Ca2+, which probably results from Ca2+ influx, as monitored by quin2 fluorescence, under stimulation with arachidonate. The concentration of N-ethylmaleimide giving a complete inhibition of Ca2+ influx was consistent with that required to inhibit collagen- or arachidonate-induced aggregation. Prostaglandin metabolism from arachidonate to thromboxane A2 was not disturbed by N-ethylmaleimide, while phosphatidate formation induced by arachidonate was slightly inhibited by it at concentrations at which aggregation was completely inhibited. These data suggest that N-ethylmaleimide preferentially suppresses increase in cytoplasmic free Ca2+ which is linked to thromboxane A2-receptor occupation in collagen- or arachidonate-stimulated platelets, probably due to blockage of Ca2+ influx through Ca2+-channel protein, thereby inhibiting aggregation induced by these agonists. 相似文献
27.
Conformational change of bovine serum albumin by heat treatment 总被引:1,自引:0,他引:1
Kunio Takeda Akira Wada Kazuo Yamamoto Yoshiko Moriyama Koichiro Aoki 《Journal of Protein Chemistry》1989,8(5):653-659
The thermal denaturation of bovine serum albumin (BSA) was studied at pH 2.8 and 7.0 in the range of 2–65°C. The relative proportions of -helix, -structure, and disordered structure in the protein conformation were determined as a function of temperature, by the curve-fitting method of circular dichroism spectra. With the rise of temperature at pH 7.0, the proportion of -helix decreased above 30°C and those of -structure and disordered structure increased in the same temperature range. The structural change was reversible in the temperature range below 45°C. However, the structural change was partially reversible upon cooling to room temperature subsequent to heating at 65°C. On the other hand, the structural change of BSA at pH 2.3 was completely reversible in the temperature range of 2–65°C, probably because the interactions between domains and between subdomains might disappear due to the acid expansion. The secondary structure of disulfide bridges-cleaved BSA remained unchanged during the heat treatment up to 65°C at pH 2.8 and 7.0. 相似文献
28.
X Wang N Sato M A Greer S E Greer S McAdams 《Biochemical and biophysical research communications》1989,163(1):471-475
The permeant molecules, urea and glycerol, evoked a prompt secretory burst of TSH and PRL when added to the extracellular medium of acutely dispersed anterior pituitary cells. Secretion of both hormones was proportional to the concentration of urea or glycerol between 26 and 104 mM (r greater than 0.89, P less than 0.001). Equivalent concentrations of the impermeant molecule, mannitol, did not induce secretion. The acute TSH and PRL secretory responses to TRH, hyposmolarity, and permeant molecules were qualitatively indistinguishable. These data support our hypothesis that cell swelling and resultant plasmalemma expansion is a potent inducer of hormone secretion. Since the secretory response to permeant molecules was not reduced in a Ca2+-free medium containing 0.1 mM EGTA, an increase in Ca2+ transport across the plasmalemma to raise cytosol Ca2+ concentration does not appear involved. 相似文献
29.
Effect of cell cholesterol content on apolipoprotein B secretion and LDL receptor activity in the human hepatoma cell line, HepG2 总被引:1,自引:0,他引:1
Human hepatoma HepG2 cells were used to study the effects of cholesterol loading and depletion on apolipoprotein B (apoB) secretion and low-density lipoprotein (LDL) receptor activity. Exposure of HepG2 cells to cholesterol and oleic acid, which elevated intracellular cholesterol levels, stimulated apoB secretion and reduced receptor-mediated uptake of LDL, whereas recombinant complexes of apolipoprotein A-I with dimyristoylphosphatidylcholine, which depleted the cellular cholesterol pool, inhibited apoB secretion and up-regulated LDL receptors. Significant negative correlation (r = -0.92, P less than 0.001) between the levels of apoB secretion and LDL uptake was found. These data suggest that the cholesterol content of the cells may induce concomitant changes in apoB secretion and LDL receptor activity. 相似文献
30.
Masa-aki Sato 《Biological cybernetics》1990,62(3):237-241
A new learning algorithm is described for a general class of recurrent analog neural networks which ultimately settle down to a steady state. Recently, Pineda (Pineda 1987; Almeida 1987; Ikeda et al. 1988) has introduced a learning rule for the recurrent net in which the connection weights are adjusted so that the distance between the stable outputs of the current system and the desired outputs will be maximally decreased. In this method, many cycles are needed in order to get a target system. In each cycle, the recurrent net is run until it reaches a stable state. After that, the weight change is calculated by using a linearized recurrent net which receives the current error of the system as a bias input. In the new algorithm the weights are changed so that the total error of neuron outputs over the entire trajectory is minimized. The weights are adjusted in real time when the network is running. In this method, the trajectory to the target system can be controlled, whereas Pineda's algorithm only controls the position of the fixed point. The relation to the back propagation method (Hinton et al. 1986) is also discussed. 相似文献