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1.
Ronald J.A. Wanders Carlo Van Roermund Cor Lof Alfred J. Meijer 《Analytical biochemistry》1983,129(1):80-87
A simple fluorimetric assay for the determination of carbamoyl phosphate in tissue extracts is described. In the assay, production of ATP from carbamoyl phosphate and ADP by carbamate kinase is coupled to the formation of NADPH, using glucose, hexokinase, NADP+, and glucose-6-phosphate dehydrogenase. Production of NADPH in this system proved to be equal to the amount of carbamoyl phosphate present. 相似文献
2.
A Merlin W Voos A C Maarse M Meijer N Pfanner J Rassow 《The Journal of cell biology》1999,145(5):961-972
Tim44 is a protein of the mitochondrial inner membrane and serves as an adaptor protein for mtHsp70 that drives the import of preproteins in an ATP-dependent manner. In this study we have modified the interaction of Tim44 with mtHsp70 and characterized the consequences for protein translocation. By deletion of an 18-residue segment of Tim44 with limited similarity to J-proteins, the binding of Tim44 to mtHsp70 was weakened. We found that in the yeast Saccharomyces cerevisiae the deletion of this segment is lethal. To investigate the role of the 18-residue segment, we expressed Tim44Delta18 in addition to the endogenous wild-type Tim44. Tim44Delta18 is correctly targeted to mitochondria and assembles in the inner membrane import site. The coexpression of Tim44Delta18 together with wild-type Tim44, however, does not stimulate protein import, but reduces its efficiency. In particular, the promotion of unfolding of preproteins during translocation is inhibited. mtHsp70 is still able to bind to Tim44Delta18 in an ATP-regulated manner, but the efficiency of interaction is reduced. These results suggest that the J-related segment of Tim44 is needed for productive interaction with mtHsp70. The efficient cooperation of mtHsp70 with Tim44 facilitates the translocation of loosely folded preproteins and plays a crucial role in the import of preproteins which contain a tightly folded domain. 相似文献
3.
The rate of proteolysis is an important determinant of the intracellular protein content. Part of the degradation of intracellular
proteins occurs in the lysosomes and is mediated by macroautophagy. In liver, macroautophagy is very active and almost completely
accounts for starvation-induced proteolysis. Factors inhibiting this process include amino acids, cell swelling and insulin.
In the mechanisms controlling macroautophagy, protein phosphorylation plays an important role. Activation of a signal transduction
pathway, ultimately leading to phosphorylation of ribosomal protein S6, accompanies inhibition of macroautophagy. Components
of this pathway may include a heterotrimeric Gi3-protein, phosphatidylinositol 3- kinase and p70S6 kinase. Recent evidence
indicates that lysosomal protein degradation can be selective and occurs via ubiquitin- dependent and -independent pathways.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
4.
Michiel L. Houben Marloes J. M. Olde Nordkamp Peter G. J. Nikkels Cornelis K. van der Ent Linde Meyaard Louis Bont 《PloS one》2013,8(12)
The soluble form of the inhibitory immune receptor leukocyte-Associated Ig-like Receptor-1 (sLAIR-1) is present in plasma, urine and synovial fluid and correlates to inflammation. We and others previously showed inflammatory protein expression in normal amniotic fluid at term. We hypothesized that sLAIR-1 is present in amniotic fluid during term parturition and is related to fetal lung function development. sLAIR-1 was detectable in all amniotic fluid samples (n=355) collected during term spontaneous deliveries. First, potential intra-uterine origins of amniotic fluid sLAIR-1 were explored. Although LAIR-1 was expressed on the surface of amniotic fluid neutrophils, LAIR-1 was not secreted upon ex vivo neutrophil stimulation with LPS, or PMA/ionomycin. Cord blood concentrations of sLAIR-1 were fourfold lower than and not related to amniotic fluid concentrations and placentas showed no or only sporadic LAIR-1 positive cells. Similarly, in post-mortem lung tissue of term neonates that died of non-pulmonary disorders LAIR-1 positive cells were absent or only sporadically present. In fetal urine samples, however, sLAIR-1 levels were even higher than in amniotic fluid and correlated with amniotic fluid sLAIR-1 concentrations. Second, the potential relevance of amniotic fluid sLAIR-1 was studied. sLAIR-1 concentrations had low correlation to amniotic fluid cytokines. We measured neonatal lung function in a convenient subset of 152 infants, using the single occlusion technique, at a median age of 34 days (IQR 30-39). The amniotic fluid concentration of sLAIR-1 was independently correlated to airway compliance (ρ=0.29, P=.001). Taken together, we show the consistent presence of sLAIR-1 in amniotic fluid, which originates from fetal urine. Concentrations of sLAIR-1 in amniotic fluid during term deliveries are independent from levels of other soluble immune mediators. The positive association between concentrations of amniotic fluid sLAIR-1 and neonatal lung compliance suggests that amniotic fluid sLAIR-1 may be useful as a novel independent marker of neonatal lung maturation. 相似文献
5.
Regulation of autotrophic metabolism in Pseudomonas oxalaticus OX1 wild-type and an isocitrate-lyase-deficient mutant 总被引:1,自引:0,他引:1
In Pseudomonas oxalaticus the activity and synthesis of the Calvin cycle enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) are regulated by inactivation and endproduct repression, respectively. Phosphoenolpyruvate (PEP) has been suggested to function as a signal molecule for the latter control system. During growth of the organism in carbon-source-limited continuous cultures with various ratios of acetate and formate in the feed, the RuBisCO levels varied considerably, but no correlation was observed with the intracellular concentrations of PEP. To study whether the repression exerted by acetate utilization was dependent on the synthesis of glycolytic intermediates from this compound, an acetate-negative mutant defective in isocitrate lyase was isolated and characterized. Clear evidence was obtained that in this mutant acetate is as effective in repressing RuBisCO synthesis as in the wild-type. It therefore appears more likely that acetyl-CoA or a closely related metabolite functions as a signal molecule in the regulation of RuBisCO synthesis. 相似文献
6.
7.
Dexamethasone regulates bile acid synthesis in monolayer cultures of rat hepatocytes by induction of cholesterol 7 alpha-hydroxylase. 总被引:2,自引:1,他引:1
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To study the effect of steroid hormones on bile acid synthesis by cultured rat hepatocytes, cells were incubated with various amounts of these compounds during 72 h and conversion of [4-14C]cholesterol into bile acids was measured. Bile acid synthesis was stimulated in a dose-dependent way by glucocorticoids, but not by sex steroid hormones, pregnenolone or the mineralocorticoid aldosterone in concentrations up to 10 microM. Dexamethasone proved to be the most efficacious inducer, giving 3-fold and 7-fold increases in bile acid synthesis during the second and third 24 h incubation periods respectively, at a concentration of 50 nM. Mass production of bile acids as measured by g.l.c. during the second day of culture (28-52 h) was 2.2-fold enhanced by 1 microM-dexamethasone. No change in the ratio of bile acids produced was observed during this period in the presence of dexamethasone. Conversion of [4-14C]7 alpha-hydroxycholesterol, an intermediate of the bile acid pathway, to bile acids was not affected by dexamethasone. Measurement of cholesterol 7 alpha-hydroxylase activity in homogenates of hepatocytes, incubated with 1 microM-dexamethasone, showed 10-fold and 90-fold increases after 48 and 72 h respectively, as compared with control cells. As with bile acid synthesis from [14C]cholesterol, no change in enzyme activity was found in hepatocytes cultured in the presence of 10 microM steroid hormones other than glucocorticoids. Addition of inhibitors of protein and mRNA synthesis lowered bile acid production and cholesterol 7 alpha-hydroxylase activity and prevented the rise of both parameters with dexamethasone, suggesting regulation at the mRNA level. We conclude that glucocorticoids regulate bile acid synthesis in rat hepatocytes by induction of enzyme activity of cholesterol 7 alpha-hydroxylase. 相似文献
8.
9.
J H Meijer 《European journal of morphology》1990,28(2-4):308-316
The suprachiasmatic nuclei of the hypothalamus contain a major circadian pacemaker. The most important external stimulus that affects the circadian pacemaker is the environmental light-dark cycle. The effects of light and darkness on the pacemaker at various phases of the circadian cycle have been well documented. In this paper these effects are summarized briefly. A number of pharmacological and neurophysiological studies will then be presented that are related to the processing of light information by the circadian system. It will be considered whether these studies have increased insight in the behavioral responsiveness to light. 相似文献
10.