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41.
Rat liver mitochondria are not fully functional at birth. The relationship between this deficiency and the affinity for phosphate, in oxidative phosphorylation or in phosphate transport, have been studied.The phosphate concentration necessary to observe maximal rate of succinate oxidation in the presence of ADP was higher for newborn than for adult rat liver mitochondria. After preincubation of newborn rat liver mitochondria with ATP, the rate of succinate oxidation in the presence of ADP increased with phosphate concentration similarly for newborn and adult rat liver mitochondria. The maximal rate of phosphate-acetate exchange, which is an indirect measure of the rate of phosphate transport across the mitochondrial membrane, was not significantly different for adult and newborn rat liver mitochondria. On the contrary the apparent affinity for phosphate was about ten-fold lower for newborn than for adult mitochondria. 相似文献
42.
Rapid increase in poly(A) (+) mRNA content following inhibition of protein synthesis 总被引:2,自引:0,他引:2
When resting 3T6 cells undergo a serum-induced transition to the growing state, the cytoplasmic content of ribosomal, transfer and messenger RNA increase as the cells prepare for DNA synthesis. The normal linear increase in mRNA content occurs even when the production of ribosomes is blocked. In this paper we determine the effect of inhibiting protein synthesis on the increase in poly(A) (+) mRNA content. Resting cells were serum stimulated in the presence of cycloheximide or puromycin at levels which inhibit protein synthesis by greater than 95%. Cytoplasmic poly(A) (+) mRNA content was determined at various times thereafter. We found that mRNA content increased five to ten times more rapidly in drug treated cells than in control cells stimulated in the absence of inhibitors. mRNA content increased 50–70% by one hour, and 60–90% by two hours following stimulation in the presence of inhibitor, and remained more or less constant thereafter. In contrast, mRNA content increased linearly in control stimulated cultures and did not double until about 15 hours after stimulation. The rapid increase in mRNA content is most likely the result of inhibition of protein synthesis rather than a secondary effect of the drug since the same observations were made in growth stimulated cells if protein synthesis was blocked with either puromycin or cycloheximide. A similar effect was also observed with resting 3T6, exponentially growing 3T6 and growing HeLa cells following exposure to cycloheximide, although the magnitude of the increase was less than that observed with growth stimulated cells. Puromycin had negligible effect on mRNA content in resting or exponentially growing cells. The rapid increase in cytoplasmic poly(A) (+) mRNA content was not due to rapid unbalanced export of nuclear poly(A) (+) RNA into the cytoplasm since there was no decrease in nuclear poly(A) content following serum stimulation in the presence of cycloheximide. 相似文献
43.
Joseph P. Stein James F. Catterall Paula Kristo Anthony R. Means Bert W. OMalley 《Cell》1980,21(3):681-687
Two thirds of the natural chicken ovomucoid gene has been sequenced, including all exons and the intron sequences surrounding all fourteen intron/ exon junctions. The junction sequences surrounding four of the introns are redundant; however, the sequences surrounding the other three introns contain no redundancies and thus the splicing sites at either end of these three introns are unambiguous. The splicing in all cases conforms to the GT-AG rule. The ovomucoid gene sequence around intron F can be used to predict the cause of an internal deletion polymorphism in the ovomucoid protein, which is an apparent error in the processing of the ovomucoid pre-mRNA. We also compare the structural organization of the ovomucoid gene with the ovomucoid protein sequence to examine theories of the evolution of ovomucoids as well as the origin of intervening sequences. This analysis suggests that the present ovomucoid gene evolved from a primordial ovomucoid gene by two separate intragenic duplications. Furthermore, sequence analyses suggest that introns were present in the primordial ovomucoid gene before birds and mammals diverged, about 300 million years ago. Finally, the positions of the introns within the ovomucoid gene support the theory that introns separate gene segments that code for functional domains of proteins and provide insight on the manner by which eucaryotic genes were constructed during the process of evolution. 相似文献
44.
Bernard L. Tucker George G. Lindesmith Quentin R. Stiles Richard K. Hughes Bert W. Meyer 《The Western journal of medicine》1977,126(3):179-183
Myocardial revascularization has been carried out by us in 67 patients 70 years of age or older. Advanced coronary artery disease was found at angiography in more than two thirds of the patients. The postoperative morbidity and mortality compare very favorably with those in younger patients. The early and late mortality in the 67 patients was 4.5 percent and 6.0 percent, respectively. Fifty-seven survivors have been followed an average of 21 months; for most patients there has been a pronounced improvement in clinical classification. Properly selected, patients of advanced age can undergo successful revascularization surgical procedures. The adequacy of function of the left ventricle, proper timing of the surgical operation and an aggressive yet realistic approach seem to be major determinants for a good result. 相似文献
45.
The cadmium, zinc, lead and copper concentrations in benthic invertebrates and sediment were determined during two consecutive winters in the Maarsseveen Lakes system. A sequential extraction procedure was applied to estimate the bioavailability of the trace metals in the sediment. Based on the trace metal analyses of organisms and sediment, it is concluded that the Maarsseveen Lakes system has background levels of cadmium, zinc, lead and copper. As the majority of metals was present in geochemically more stable sediment phases, the sequential extractions provided limited additional information on trace metal bioavailability. 相似文献
46.
47.
Summary High Performance Liquid Chromatography analysis of algal pigments from inter- and subtidal (deep and shallow) sediments from the Kerguelen Islands showed clear differences in the pigment composition at the different stations. High concentrations of chlorophyll c and fucoxanthin were present at all locations, indicating significant diatom densities, chlorophyll b was detected at all sites. At one station the other green algal pigments were also present; here green algae contributed more to chlorophyll a concentrations than diatoms, as estimated by using pigment ratios and microscopic observations. At another location chlorophyll b was associated with a high concentration of diadinoxanthin, indicating an abundance of euglenoids. This indicates that chemotaxonomy can be powerful tool in microphytobenthos studies since enumeration of living cells are difficult as many algae are attached to sediment particles (epipsammic algae). Ways of diagenesis, carotenoid degradation and the role of grazing are briefly mentioned. Phaeophorbide a-like pigments were the most significant chlorophyll a degradation products, with concentrations up to 110 g · g–1 dry weight sediment, i.e. 10 times the chlorophyll a concentration. Some taxonomic estimations, based on pigments ratios, and their limits, are discussed. 相似文献
48.
Horse liver contains previously unrecognized isozymes of alcohol dehydrogenase. In contrast to the molecular forms identified up to now, under the conditions employed these variants migrate toward the anode on starch gel electrophoresis and were separated from the cathodic isozymes by DEAE-cellulose chromatography. They were then purified on agarose-hexane-AMP. Their physicochemical and compositional characteristics are similar to those x alcohol dehydrogenases from human liver. Like these and similar ones from simian liver, they retain most of their activity in the presence of10
mm 4-methylpyrazole, oxidize short-chain primary alcohols very poorly, and appear to prefer longer chain primary alcohols and -hydroxy fatty acids as substrates. 相似文献
49.
Eric P. Krenning Roel Docter Bert Bernard Theo Visser Georg Hennemann 《FEBS letters》1982,140(2):229-233
50.
Litwin SB Mitra SK Von Colditz R Colditz JV Hamilton LB McManus T Jume'an HG Lazerson J 《Cardiovascular diseases》1981,8(3):364-371
The use of a fixed dosage schedule was compared with the use of activated clotting time (ACT) for determining heparin and protamine dosages during and after cardiopulmonary bypass disease. Use of the ACT resulted in a statistically significant increase in heparin dosage and a statistically significant reduction of postoperative blood loss. With ACT use, chest tubes were retained for a shorter period of time, and the incidence of serious postoperative hemorrhage was reduced from 44% to 18%. These results confirm the superiority of the ACT method for monitoring intraoperative anticoagulation in pediatric patients with congenital heart disease. 相似文献