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1.
We reported evidence that horseradish peroxidase (HRP) and chloroperoxidase (CPO) catalyze oxygen transfer from H2O2 to thioanisoles [Kobayashi, S., Nakano, M., Goto, T., Kimura, T., & Schaap, A. P. (1986) Biochem. Biophys. Res. Commun. 135, 166-171]. In the present paper, the reaction mechanism of this oxygen transfer is discussed. The oxidation of para-substituted thioanisoles by HRP compound II showed a large negative rho value of -1.46 vs. the sigma + parameter in a Hammett plot. These results are in accord with the formation of a cation radical intermediate in the rate-determining step. Hammett treatments for HRP- and CPO-dependent S-oxygenations did not provide unequivocal proofs to judge the reaction mechanism, because of the poor correlations for sigma + and sigma p parameters. Different behavior was found in kinetics and stereoselectivity between the two enzymes. Results in the present study and recent studies strongly suggested the formation of a cation radical intermediate. The oxygen atom would transfer by reaction of compound II and the cation radical intermediate. Although involvement of the cation radical was not confirmed in the CPO system, a similar mechanism was proposed for CPO. 相似文献
2.
Abstract. Cell aggregation in Dictyostelium discoideum is a chemotactic process mediated by cyclic adenosine monophosphate (CAMP), which is detected by cell surface receptors. The cAMP signal is degraded by cAMP phosphodiesterase. The possibility that cAMP signals are also used for cell communication in the multicellular stages was studied by determining whether the cAMP receptors, which are essential for signal transduction, continue to function in these stages. During slug migration, the number of binding sites per cell decreases to about 15% of the maximum level acquired during aggregation. At the onset of fruiting body formation, a three- to Four-Fold increase in cAMP binding activity occurs. This increase coincides with an increase in cAMP phosphodiesterase. Both phenomena suggest that cell-cell communication mediated by cAMP is used during culmination. During both slug migration and early culmination, the prestalk cells exhibit about twice as much binding activity as the prespore cells. 相似文献
3.
Summary Among all the Jewish families with Hunter patients in Israel, 10 were Ashkenazi or Moroccan in origin. In those families, there was a paucity of new mutations. In addition, a significant deviation of the segregation ratio between the Hunter gene and the normal allele was demonstrated among the offspring of heterozygous mothers or siblings of affected children in these families. These results confirm and extend our previous observations suggesting selection in favor of the X chromosome carrying the Hunter allele among Ashkenazi and Moroccan Jews. 相似文献
4.
The relationship between NADPH-dependent lipid peroxidation and degradation of cytochrome P-450 in adrenal cortex mitochondria 总被引:2,自引:0,他引:2
J Klimek A P Schaap T Kimura 《Biochemical and biophysical research communications》1983,110(2):559-566
The relationship between NADPH-dependent lipid peroxidation and the degradation of cytochrome P-450 has been studied in bovine adrenal cortex mitochondria. Malondialdehyde formation is accompanied by a corresponding decrease in total cytochrome P-450 content. Inhibitors of lipid peroxidation also prevent the loss of cytochrome P-450, further demonstrating a direct relationship between NADPH-dependent lipid peroxidation and degradation of P-450. To differentiate between cytochrome P-450(11)beta and P-450scc, steroid-induced difference spectra were used to evaluate P-450 degradation. These measurements provide the first evidence that both P-450's are degraded during NADPH-dependent lipid peroxidation with P-450(11)beta being much more susceptible to this process. 相似文献
5.
6.
A slow sustained increase in cytosolic Ca2+ levels mediates stalk gene induction by differentiation inducing factor in Dictyostelium. 下载免费PDF全文
During Dictyostelium stalk cell differentiation, cells vacuolate, synthesize a cellulose cell wall and die. This process of programmed cell death is accompanied by expression of the prestalk gene ecmB and induced by the differentiation inducing factor DIF. Using cell lines expressing the recombinant Ca2+-sensitive photoprotein apoaequorin, we found that 100 nM DIF increases cytosolic Ca2+ ([Ca2+]i) levels from approximately 50 to 150 nM over a period of 8 h. The Ca2+-ATPase inhibitor 2,5-di(tert-butyl)-1,4-hydroquinone (BHQ) induced a similar increase in [Ca2+]i levels and induced expression of the prestalk gene ecmB to the same level as DIF. The [Ca2+]i increases induced by DIF and BHQ showed similar kinetics and preceded ecmB gene expression by approximately 1-2 h. The Ca2+ chelator 1,2-bis(o-aminophenoxy)-ethane-N,N,N'N'-tetra-acetic acid (BAPTA) efficiently inhibited the BHQ-induced [Ca2+]i increase and blocked DIF-induced expression of the ecmB gene. These data indicate that the effects of DIF on stalk gene expression are mediated by a sustained increase in [Ca2-]i. Sustained [Ca2+]i elevation mediates many forms of programmed cell death in vertebrates. The Dictyostelium system may be the earliest example of how this mechanism developed during early eukaryote evolution. 相似文献
7.
There is growing evidence to support some form of light-activated phosphoinositide signal transduction pathway in the mammalian retina. Although this pathway plays no obvious role in mammalian phototransduction, mutations in this pathway cause retinal degenerations in Drosophila. These include the retinal degeneration A mutant, which is caused by an alteration in an eye-specific diacylglycerol kinase (DAGK) gene. In our efforts to consider genes mutated in Drosophila as candidates for mammalian eye disease, we have initially determined the map position of three DAGK genes in the mouse. 相似文献
8.
The possible involvement of oscillatory cAMP signaling in multicellular morphogenesis of the cellular slime molds 总被引:5,自引:0,他引:5
The involvement of pulsatile chemoattractant emission and signal relay in aggregation and multicellular morphogenesis of a variety of cellular slime mold species was investigated. The species differ from each other in the developmental stage when pulsatile signaling first becomes evident. In D. discoideum, D. mucoroides, and D. purpureum pulsatile signal emission starts in the preaggregative field. In D. vinaceo-fuscum, D. mexicanum, P. violaceum, and P. pallidum the aggregation centers shifts from continuous to pulsatile secretion of chemoattractant during the aggregation process. In D. minutum pulsatile signaling starts after the completion of aggregation and slightly before the onset of culmination. Tip formation is a consequence of continued attraction of amoebae inside the aggregate to the center of signal emission. The occurrence of pulsatile signaling at an early stage of development is correlated with the capacity of the tip (signaling center) to organize a relatively large number of cells into a single fruiting body. Several lines of evidence suggest that cAMP is probably involved in the coordination of morphogenetic movement in the multicellular stage of all investigated species. 相似文献
9.
An analysis of previous spontaneous abortions and the frequencies of blood-group combinations in mother-child pairs was carried out in 500 gravidae. The rate of previous spontaneous abortions in blood-group-O women whose latest child has blood group B is significantly higher than in all other women. On the other hand, the combination mother B/child AB is rarer than expected, but no increase in the rate of previous spontaneous abortions is obvious among these women. These discrepancies are interpreted as an indication that prenatal selection associated with ABO incompatibility may operate at various stages from fertilization through pregnancy, and that different incompatible combinations may be subject to selection at different stages. 相似文献
10.
The role of the tubulin-microtubule system was examined in human peripheral blood leukocytes after activation with phytohemagglutinin (PHA). Soluble tubulin and microtubules were measured with a [(3)H]colchicine-binding assay. It was found that the tubulin content of PHA-activated lymphocytes was consistently increased relative to total protein content after 36 h of culture. There was no increase in the proportion of total tubulin synthesis which was present as microtubules at 36 h. Nevertheless, as a result of increased tubulin synthesis, there was a two-to three-fold increase in total microtubular mass. Colchicine, which disrupts microtubles, was used to assess the role of microtubule assembly in the sequence of events which follow lymphocyte activation, namely lymphokine release, protein synthesis, RNA synthesis, and DNA synthesis. Colchicine consistently inhibited DNA synthesis but did not inhibit release of the lymphokine, osteoclast activating factor (OAF). Protein and RNA syntheses were inhibited much less than DNA synthesis. The fact that some effects of PHA on lymphocytes appear to require intact microtubules and at least one does not suggest that the microtubule dependent step in PHA-stimulated lymphocyte activation occurs at a stage after propagation of the signal from the membrane to the cell interior. 相似文献