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44.
External cadmium and internal calcium block of single calcium channels in smooth muscle cells from rabbit mesenteric artery. 总被引:3,自引:0,他引:3
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The patch clamp technique was used to record unitary currents through single calcium channels from smooth muscle cells of rabbit mesenteric arteries. The effects of external cadmium and cobalt and internal calcium, barium, cadmium, and magnesium on single channel currents were investigated with 80 mM barium as the charge carrier and Bay K 8644 to prolong openings. External cadmium shortened the mean open time of single Ca channels. Cadmium blocking and unblocking rate constants of 16.5 mM-1 ms-1 and 0.6 ms-1, respectively, were determined, corresponding to dissociation constant Kd of 36 microM at -20 mV. These results are very similar to those reported for cardiac muscle Ca channels (Lansman, J. B., P. Hess, and R. W. Tsien. 1986. J. Gen. Physiol. 88:321-347). In contrast, Cd2+ (01-10 mM), when applied to the internal surface of Ca channels in inside-out patches, did not affect the mean open time, mean unitary current, or the variance of the open channel current. Internal calcium induced a flickery block, with a Kd of 5.8 mM. Mean blocking and unblocking rate constants for calcium of 0.56 mM-1 ms-1 and 3.22 ms-1, respectively, were determined. Internal barium (8 mM) reduced the mean unitary current by 36%. We conclude that under our experimental conditions, the Ca channel is not symmetrical with respect to inorganic ion block and that intracellular calcium can modulate Ca channel currents via a low-affinity binding site. 相似文献
45.
Oxidation of carbon monoxide and methane by Pseudomonas methanica. 总被引:18,自引:0,他引:18
The oxidation of carbon monoxide and methane by suspensions and ultrasonic extracts of Pseudomonas methanica was studied. A continuous assay for the oxidation of CO to CO2 was devised, using O2 and CO2 electrodes in combination. Stoicheiometries of CO-dependent CO2 formation, O2 consumption and NADH oxidation, and the partial stoicheiometries of methane-dependent NADH oxidation, suggest the involvement of a mono-oxygenase in these oxidations. Evidence is presented suggesting methane and CO oxidation are catalysed by a single enzyme system, distinct, at least in part, from the NADH oxidase present in extracts. Ethanol was able to provide the reductant necessary for CO oxidation by cell suspensions, though the metabolism of ethanol by P. methanica was found unlikely to result in substrate-level formation of NADH; the means whereby alcohol oxidation could supply reductant for the mono-oxygenase are discussed. 相似文献
46.
Pathways leading to and from serine during growth of Pseudomonas AM1 in C1 compounds or succinate 总被引:1,自引:1,他引:0
1. The following enzymes of the phosphorylated pathway of serine biosynthesis have been found in methanol- and succinate-grown Pseudomonas AM1: phosphoglycerate dehydrogenase, phosphoserine-alpha-oxoglutarate aminotransferase and phosphoserine phosphohydrolase. Their specific activities were similar in the organism grown on either substrate. 2. A procedure for preparation of auxotrophic mutants of Pseudomonas AM1 is described involving N-methyl-N'-nitro-N-nitrosoguanidine as mutagen and a penicillin enrichment step. 3. A mutant, M-15A, has been isolated that is unable to grow on methanol and that lacks phenazine methosulphate-linked methanol dehydrogenase. The mutant is able to grow on methylamine, showing that the amine is not oxidized by way of methanol. 4. Loss of methanol dehydrogenase activity in mutant M-15A led to loss of phenazine methosulphate-linked formaldehyde dehydrogenase activity showing that the same enzyme is probably responsible for both activities. 5. A mutant, 20B-L, has been isolated that cannot grow on any C(1) compound tested but can grow on succinate. 6. Mutant 20B-L lacks hydroxypyruvate reductase, and revertants that regained the ability to grow on methanol, methylamine and formate contained hydroxypyruvate reductase activity at specific activities similar to that of the wild-type organism. This shows that hydroxypyruvate reductase is necessary for growth on methanol, methylamine and formate but not for growth on succinate. 7. The results suggest that during growth of Pseudomonas AM1 on C(1) compounds, serine is converted into 3-phosphoglycerate by a non-phosphorylated pathway, whereas during growth on succinate, phosphoglycerate is converted into serine by a phosphorylated pathway. 相似文献
47.
Oxygenation of methane by methane-grown Pseudomonas methanica and Methanomonas methanooxidans
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1. Experimental conditions have been found in which small amounts of methanol (approximately 2.5mm) accumulated when washed cell suspensions of methane-grown Pseudomonas methanica and Methanomonas methanooxidans were incubated with methane+oxygen mixtures in Warburg flasks. 2. The methanol formed could be separated completely from water by fractional distillation through glass helices followed by gas chromatography using 20% polyethylene glycol 400 on a Celite 545 support. 3. By using 18O-enriched oxygen gas the abundance of 18O in the methanol formed from oxidation of methane was measured with a Perkin–Elmer 270 combined gas chromatograph/mass spectrometer. The results showed that the oxygen in methanol was derived exclusively from gaseous oxygen in both micro-organisms. 4. Control experiments using [18O]water in incubation mixtures confirmed that there was negligible incorporation of the oxygen atom from water into methanol. 相似文献
48.
Nucleotide sequence analysis of the lemur beta-globin gene family: evidence for major rate fluctuations in globin polypeptide evolution 总被引:1,自引:0,他引:1
Lemur beta-related globin genes have been isolated and sequenced. Orthology
of prosimian and human epsilon-, gamma-, and beta-related globin genes was
established by dot-matrix analysis. All of these lemur globin genes
potentially encode functional beta-related globin polypeptides, though
precisely when the gamma-globin gene is expressed remains unknown. The
organization of the 18-kb brown lemur beta-globin gene cluster (5'
epsilon-gamma-[psi eta-delta]-beta 3') is consistent with its evolution by
contraction via unequal crossing-over from the putative ancestral mammalian
beta-globin gene cluster (5' epsilon-gamma- eta-delta-beta 3'). The dwarf
lemur nonadult globin genes are arranged as in the brown lemur. Similar
levels of synonymous (silent) nucleotide substitutions and noncoding DNA
sequence differences have accumulated between species in all of these
genes, suggesting a uniform rate of noncoding DNA divergence throughout
primate beta-globin gene clusters. These differences are comparable with
those observed in the nonfunctional psi eta pseudogene and have therefore
accumulated at the presumably maximal neutral rate. In contrast,
nonsynonymous (replacement) nucleotide substitutions show a significant
heterogeneity in distribution for both the same gene in different lineages
and different genes in the same lineage. These major fluctuations in
replacement but not silent substitution rates cannot be attributed to
changes in mutation rate, suggesting that changes in the rate of globin
polypeptide evolution in primates is not governed solely by variable
mutation rates.
相似文献
49.
Choice between autotrophy and heterotrophy in Pseudomonas oxalaticus. Growth in mixed substrates
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1. The type of metabolism adopted by Pseudomonas oxalaticus during growth on a variety of carbon sources was studied. 2. The only substrate upon which autotrophic growth was observed is formate. 3. In mixtures of formate and those substrates upon which the organism can grow faster than on formate, e.g. succinate, lactate or citrate, heterotrophic metabolism results. 4. In mixtures of formate and those substrates upon which the organism can grow at a similar rate to that on formate, e.g. glycollate or glyoxylate, the predominant mode of metabolism adopted is heterotrophic utilization of the C2 substrate coupled with oxidation of formate as ancillary energy source. 5. P. oxalaticus grows on oxalate 30% slower than on formate. In mixtures of formate and oxalate, the predominant mode of metabolism adopted is autotrophic utilization of formate coupled with oxidation of oxalate as ancillary energy source. 6. In mixtures of formate and those substrates upon which the organism grows at a much lower rate than on formate, e.g. glycerol and malonate, the predominant mode of metabolism adopted is autotrophic utilization of formate. 7. It is concluded that synthesis of the enzymes involved in autotrophic metabolism is controlled by a combination of induction and metabolite repression. 相似文献
50.