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121.
Inhibition of protein synthesis by Cl-   总被引:17,自引:0,他引:17  
Optimum K+ concentration for protein synthesis in four eukaryotic cell-free systems is obtained with 70 to 80 mM added KCl or with 110 to 150 mM added K(OAc). The different K+ optima are due to inhibition of protein synthesis by Cl- at concentrations higher than those present in the cytoplasm of eukaryotic cells. Initiation of protein synthesis is severely inhibited with 150 mM added KCl. This inhibition results from an impairment of mRNA binding to ribosomes. The binding of initiator Met-tRNAt, however, is only slightly inhibited by 150 mM KCl.  相似文献   
122.
The optical isomers of (±)r-7,t-8-dihydroxy-7,8-dihydrobenzo[a]pyrene and its synthetic precursor (±)r-7,t-8-dihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene were resolved as their di-(−)menthoxyacetates using high-pressure liquid chromatography. Saponification of the resolved diesters yielded the corresponding enantiomers. The specific rotation, CD spectra, and ORD curves are reported. The resolution of these optical isomers permits detailed studies on the enzymatic intermediates and the mechanism of benzo[a]pyrene activation to its carcinogenic form. The method is of general usefulness for the resolution of optical isomers.  相似文献   
123.
Limited chymotryptic cleavage of soluble chicken gizzard desmin protofilaments allows the characterization of three structurally distinct domains. A surface-exposed very basic amino-terminal region (the headpiece) with an amino acid sequence excluding a-helical organization (7.5 kd) is separated from the perhaps globular carboxy-terminal 48 residues (the tailpiece) by a distinctly different middle domain of approximately 330 residues. This 38 kd domain is very rich in α-helix (at least 83%), and electron microscopy reveals a thin rod with a length of 500 ± 50 Å. Amino acid sequence data also show that the rod domain is interrupted by a nonhelical portion. An a-helical array is able to form a coiled-coil spanning the carboxy-terminal half of the 38 kd domain. The a-type diffraction pattern of 10 nm filaments arises from a coiled-coil conformation displayed through most but not all of the middle domain of the protofilaments.  相似文献   
124.
Starting from the spectrophotometric method, described in ADELMAN et al., optimal reaction conditions for the measurement of fructokinase (ketohexokinase) in pig liver were systematically studied. It was necessary to increase the concentration of the substrate and further to lower the concentration of ATP for an optimal Mg: ATP-radio of 2:1. Using the optimized method fructokinase activity was determined in pig liver in relation to age, beginning from the last days of pregnancy to puberty. In liver of fetuses and newborn piglets during the first two days of life no or only a minute activity of the fructokinase was recorded. Therefore, the high level of fructose in fetal blood results from the inability of the fetus to metabolize fructose synthezised in the placenta or the fetal organs. At the end of the first week of life the activity of fructokinase was 10 times, after the second week 15-20 times higher than at birth. This high level remains constant during the suckling period and after weaning. For this reason, piglets after the first week of life are able to metabolize fructose and after the third week to form glucose and to release it into circulation. In adult pigs the activity of fructokinase in the liver decreases slightly. It corresponds-as in rat and human-to the elimination rate of experimentally applied fructose from the circulation. Therefore, this enzyme even in pigs is of significant importance for the utilization of fructose.  相似文献   
125.
Deoxycytidine kinase activity in normal rat liver cytosol was low (0.8 nmol/hr/mg protein); it increased 2–26-fold in 12 lines of chemically-induced, transplantable rat hepatomas of different growth rates. The increased kinase activity correlated positively with the hepatoma growth rate. The kinase activity did not change in the regenerating liver and the activity in the differentiating, neonatal rat liver was similar to values in adult liver. Deoxycytidine kinase activity in 2 chemically-induced, transplantable rat kidney tumors was increased to twice the value found in normal renal cortex. Among 15 normal rat tissues examined the highest kinase activities were observed in thymus, bone marrow and spleen. Of the normal and malignant rat tissues tested, only testis had detectable cytidine deaminase activity.  相似文献   
126.
127.
Lung degassing: an evaluation of two methods   总被引:1,自引:0,他引:1  
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128.
129.
Summary The yields of dipeptide obtained from the reaction of 0.2M 2(3)-O-(glycyl)-adenosine-5-(O-methylphosphate) and 0.2M amino acid at pH 8.2 ranged from 0.1% to 35.5% for a group of 15 amino acids. The yields of glyser (35.3%), gly-cys (11.8%) and gly-thr (5.4%) were considerably greater than dipeptide yields obtained from any of the other 12 amino acids ( 1.7%). Aminolysis of 0.05M 2(3)-O-(glycyl)-adenosine-5-(O-methylphosphate) by 0.4M serine ethyl ester yielded 53% glycylserine diketopiperazine, via N-(glycyl)-serine ethyl ester as a transient intermediate. The prebiotic significance of these reactions is discussed.Abbreviations MepA adenosine-5-(O-methylphosphate) - MepA-gly 2(3)-O-(glycyl)-adenosine-5-(O-methylphosphate) - DKP diketopiperazine - serOEt serine ethyl ester - gly-serOEt N-(glycyl)-serine ethyl ester - Boc-gly N-tertbutyloxycarbonylglycine - cyclo-(gly-ser-) glycylserine diketo-piperazine - O-gly-ser O-glycylserine - O-(gly)-gly-ser O-(glycyl)-glycylserine - gly-ser N-glycylserine  相似文献   
130.
Histone modifications in the yeast S. Cerevisiae.   总被引:11,自引:5,他引:6       下载免费PDF全文
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