Tin compounds are being used increasingly inin industry and in medicine. There have been relatively few studing term biological effects of this metal, although acute effects hcumented. In this report we describe experiments which show thastannous chloride, is readily taken up by human white blood cellsan cause damage to DNA. Damage was detected in WBC after e-50 μM tin(II) for 30 min at either 0°C or 37°C. The amount oserved was more extensive than that produced by exposure of nolar amounts of chromium(VI), a known carcinogen and DNAagent. Additional indication of cellular damage is that exposmn lymphocytes or mouse splenocytes to tin(II) interfered with theio be stimulated by the polyvalent mitogen concanavalin A (Con A). rast, tin(IV) was not taken up by cells, did not cause DNA damage nor dinhibit stimulation of DNA synthesis in cells that were exposed to Con A. 相似文献
The nonenzymic hydrolysis of and were studied by infrared (IR) spectroscopy. Protons resulting from hydrolysis of ATP are not bound to the N1 atoms of the adenine residues. With hydrolysis of , these protons are partially bound to the terminal phosphate group of ADP, namely, , , , and , present after hydrolysis. With decreasing pH or when Mg2+ ions are present, all hydrolysis protons are attached to the orthophosphate molecules.With hydrolysis of the pH decreases up to 40% degree of hydrolysis. Then the system becomes self-buffered in the physiological pH region. A similar pH decrease is found with hydrolysis of . With these systems, however, the pH decreases slightly also at degrees of hydrolysis larger than 40%. No other systems show pronounced pH changes during hydrolysis; in other words, they are buffer systems.The IR bands demonstrate that mesomeric bond resonance in the phosphate groups strongly depends on whether protons are present at these groups. Regarding the equilibria of proton attachment mentioned above, mesomeric bond resonance in these groups strongly depends on pH and on the presence of ions.With hydrolysis of ATP, two POH groups are formed that bind H2O molecules via strong hydrogen bonds, changing the solvate structure. Finally, easily polarizable hydrogen bonds are formed, for instance, bonds with the hydrolysis of , and bonds with the hydrolysis of . These bonds strongly interact with their environment. The formation of these hydrogen bonds strongly depends on pH and the presence of ions.All these effects, especially the intermolecular ones, contribute to the change of free energy during ATP hydrolysis. 相似文献
N-Acetylneuraminate synthase from 6OE catalyzes the conversion of phosphoenolpyruvate and 2-acetamido-6-azido-2,6-dideoxy--mannose into 5-acetamido-9-azido-3,5,9-trideoxy-----2-nonulosonic acid. The product, a 9-azido-9-deoxy derivative of N-acetylneuraminic acid, is indistinguishable from a chemically synthesized sample by i. the thiobarbituric acid assay, ii. paper electrophoresis, and iii. paper electrophoresis following sodium borohydride reduction. Both the chemically and the enzymically synthesized samples are substrates of the reaction catalyzed by CTP:CMP-N-acetylneuraminate cytidylyl-transferase from 6OE 相似文献
The self-association of the bacteriophage T4 gene 32 protein has been examined in the analytical ultracentrifuge under varying conditions to determine the nature of the process. The process is not a simple indefinite association with one association constant (monomer dimer trimer etc.). The complexity of the process is shown by (1) peculiarities in the molecular weight versus concentration curves, in the region of the dimer (observed with increasing ionic strength, at pH 10, in 0.04 m-MgCl2, with aged preparations, at 19 °C and in the presence of the oligonucleotide d(pT)10), (2) the increased sigmoidicity of the association curve in the presence of glycerol or oligo[d(pT)4], and (3) the discontinuity in the association curve at the tetramer at a pH value of approximately 9.4. A model with two association constants which could vary independently (monomer dimer tetramer etc.) explained many of the findings. However, a more complex model was required to explain curves which had a plateau at the dimer with increased association at higher protein concentrations. Thus, under all conditions examined there is evidence for more than one type of protein-protein interaction. These different interactions may be involved in a physiological function such as recombination. 相似文献
A genetic and sequence analysis of 373 ICR-191-induced mutations in the lacI gene of Escherichia coli reveals that 365 of the mutations (97·9%) are frameshifts involving the addition or deletion of a single base-pair from a sequence including, in one case, a sequence. Some of the remaining eight mutations (2·1%) represent the loss or gain of a base-pair from a sequence. Certain mutational sites are relative hotspots for ICR-191-induced mutations, and we have analyzed the role of surrounding sequences on relative mutation rates. The preference for +1 frameshifts or ?1 frameshifts is site-specific, so that at some sites +1 frameshifts predominate by a 10:1 ratio, whereas at other sites ?1 frameshifts are favored by an approximately 2:1 ratio. The characterized frameshift mutations in lacI described here are useful for constructing systems to detect other frameshift and deletion mutations. 相似文献
Absorption changes invoked by short flashes in the Soret band region were measured in the thermophilic cyanobacterium Synechococcus sp. and photoresponses of P-700, cytochrome c-553 and cytochrome f were resolved with the aid of a microcomputer. Cytochrome c-553 was oxidized very rapidly with a half-time of less than 20 μs, while the half oxidation time of cytochrome f was 35–45 μs. The two cytochromes were reduced monophasically with half-time of 2 ms after a lag lasting a few milliseconds. The reduction kinetics of P-700 showed three exponential phases with half-times of 40 μs, 200 μs and 2 ms, which are ascribed to electron donation from cytochrome f, the Rieske iron-sulfur protein and plastoquinone, respectively. The results support the following sequence and rates of linear electron transport at the physiological temperature of the cyanobacterium: P-700 cytochrome c-553 cytochrome f Rieske protein plastoquinone. 相似文献
