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961.
J I de Vicente P del Valle F Busto D de Arriaga J Soler 《Biochemistry international》1991,24(2):339-347
High concentrations of either Mg-ATP complex, free ATP, or free Mg2+ ions were inhibitors of the mitochondrial F1-ATPase moiety from Phycomyces blakesleeanus. Free Mg2+ acts as a linear competitive inhibitor with regard to Mg-ATP hydrolysis with a Ki value of 2.8 mM. The inhibition by free ATP was markedly biphasic and thus simple competitive inhibition alone is not sufficient to explain the inhibitory effect. From these results conclusions were drawn about the binding of the substrate, Mg-ATP complex, to the enzyme. 相似文献
962.
J I de Vicente P del Valle F Busto D de Arriaga J Soler 《Biochimie et biologie cellulaire》1991,69(7):454-459
Mitochondrial F1-ATPase was purified from the mycelium of Phycomyces blakesleeanus NRRL 1555(-) and its kinetic characteristics were studied. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the enzyme reveals five bands (alpha, beta, gamma, delta, and epsilon) characteristic of the F1 portion with apparent molecular weights of 60,000, 53,000, 31,000, 25,000, and 21,000, respectively. The molecular weight of the native F1-ATPase from Phycomyces blakesleeanus was in agreement with the stoichiometry alpha 3 beta 3 gamma delta epsilon. The MgATP complex is the true substrate for ATPase activity which has a Km value of 0.15 mM. High concentrations of free ATP or free Mg2+ ions inhibit the ATPase activity. ADP appears to act as a negative allosteric effector with regard to MgATP hydrolysis, with the apparent Vmax remaining unchanged. 相似文献
963.
Anacamptis pyramidalis is a variable and wide-spread European-Mediterranean taxon. Beside a dominant cytotype with 2n = 36 it includes cytotypes with 2n = 54 and 63 in northern Tuscany (and the Eastern Pyrenees) and one with 2n = 72 on Malta. In contrast,A. urvilleana, formerly often misidentified and included inA. pyramidalis, is a monomorphic and distinct species, endemic to the Maltese Islands. It has 2n = 36, can be clearly separated by morphological and anatomical features and is isolated from partly sympatric populations ofA. pyramidalis with 2n = 72 by differences in chromosome number, flowering time and habitat preference. 相似文献
964.
It is known from previous investigations that dry lichens with green algae are able to recover net photosynthesis through rehydration with water vapor, whereas all blue-green lichens tested so far lack this ability. The REM micrographs of the present study show that the green phycobionts (Trebouxia spec.) of Ramalina maciformis become turgid only after water vapor uptake. In contrast, the blue-green phycobionts (Nostoc spec.) of Peltigera rufescens do not differ in appearance from the dry state, even when the thallus has reached equilibrium with the water vapor-saturated air; they require liquid water for turgidity. It is hypothesized that, after humidity hydration, water content is not sufficient for reestablishment of a functioning osmotic cell system in the blue-green phycobiont. 相似文献
965.
The effects of fatigue on diaphragmatic contractility in vivo are unknown. In this study we used sonomicrometry to examine the velocity of shortening and lengthening and the amount of shortening in the fresh and fatigued canine hemidiaphragm (8 dogs) including the force generated. Fatigue was produced by epiphrenic stimulation of the left phrenic nerve; the right hemidiaphragm acted as the control. We found that 1) hemidiaphragmatic fatigue caused an increase in frequency with reduced tidal volume; 2) fatigue resulted in a near complete cessation of tidal shortening during spontaneous breathing; 3) there was an initial decrease in central activation (electromyogram) to the fatigued hemidiaphragm, an indication of central fatigue; 4) force-frequency curves showed a considerable and prolonged loss of the amount of shortening, velocity, and force generated by the fatigued hemidiaphragm during supramaximal stimulation, an indication of peripheral fatigue; and 5) during spontaneous breathing in the fatigued hemidiaphragm, tidal shortening remained reduced for up to 3 h, whereas in the right right hemidiaphragm tidal shortening and electromyographic activity did not change. We conclude that fatigue of a hemidiaphragm alters the spontaneous breathing pattern and produces profound modifications in its contractile properties without altering contralateral hemidiaphragmatic performance. 相似文献
966.
Molecular evidence for the rapid propagation of mouse t haplotypes from a single, recent, ancestral chromosome 总被引:11,自引:0,他引:11
Silver LM; Hammer M; Fox H; Garrels J; Bucan M; Herrmann B; Frischauf AM; Lehrach H; Winking H; Figueroa F 《Molecular biology and evolution》1987,4(5):473-482
Mouse t haplotypes are variant forms of chromosome 17 that exist at high
frequencies in worldwide populations of two species of commensal mice. To
determine both the relationship of t haplotypes to each other and the
species within which they exist, 35 representative t haplotypes were
analyzed by means of 10 independent molecular probes, including five DNA
clones and five polypeptide spots identified by means of two- dimensional
gel electrophoresis. All of the tested haplotypes were found to share
restriction fragments and polypeptide spots that are absent in mice
carrying wild-type forms of chromosome 17. This observation provides the
first direct evidence that all of the known t haplotypes are descendents of
a single ancestral chromosome. The absence of variation among t haplotypes
could mean that this ancestral chromosome existed relatively recently, in
which case it would be necessary to postulate introgressions of t
haplotypes across species lines to explain their presence in both Mus
domesticus and M. musculus. Alternatively, it is possible that the
ancestral chromosome existed prior to the split between M. domesticus and
M. musculus and that, by chance, our probes fail to detect polymorphisms
that exist among the t haplotypes. A further result of our analysis is the
characterization of a partial t haplotype in a wild population of Israeli
mice.
相似文献
967.
Three regions in the DNA of plasmid pLS1 show sequence-directed static bending. 总被引:5,自引:1,他引:4 下载免费PDF全文
J Pérez-Martín G H del Solar A G de la Campa M Espinosa 《Nucleic acids research》1988,16(19):9113-9126
Three regions showing abnormal electrophoretic mobility, which is an indication of the existence of bends in DNA, have been observed in the DNA of plasmid pLS1. These loci have been characterized by assays designed to detect sequence-directed bending in DNA (temperature-dependence migration and two dimensional electrophoresis). The first region (locus B-1) was located within a fragment that contains a proposed inhibitor countertranscribed RNA (RNAII). The second locus (B-2) contains the plasmid plus origin of replication and the third region (locus B-3) was located in the vicinity of a putative antisense RNA (RNAI) of unknown function. The centres of the first two bent DNA regions were located by circular permutation assays at nucleotides 882 (locus B-1) and 634 (locus B-2). The bend centre of locus B-1 was found to be upstream of the promoter for the putative antisense RNAII. The centre of curvature in locus B-2 was located in the vicinity of the putative promoter of the replication proteins RepA and RepB and of a sequence that has three 11-bp direct repeats. The DNA sequence at this region showed the existence of A.T tracts, with an internal repeat of 10 to 11 base pairs, for five helix turns. A complex curvature in the DNA of pLS1 at locus B-2 that may have a regulatory role in plasmid replication is postulated. 相似文献
968.
969.
M Miranda C di Ilio A Bonfigli A Arcadi G Pitari S Dupre G Federici G del Boccio 《Biochimica et biophysica acta》1987,913(3):386-394
The actions of glutathione S-transferase and tyrosinase on the in vitro production of glutathionyl-3,4-dihydroxyphenylalanine and the dopachrome level in the presence of GSH and L-3,4-dihydroxyphenylalanine were studied. No clear evidence of complementarity between tyrosinase and glutathione S-transferase was observed; on the contrary, in the presence of glutathione S-transferase the glutathionyl-3,4-dihydroxyphenylalanine yield was lower than with tyrosinase only, as measured by HPLC. It is concluded that the spontaneous conjugation of GSH with dopaquinone should probably be high enough to scavenge the toxic quinone and to produce precursors for phaeomelanogenesis. 相似文献
970.
Effects of D-serine on bacterial D-amino acid transaminase: accumulation of an intermediate and inactivation of the enzyme 总被引:1,自引:0,他引:1
A Martinez del Pozo M A Pospischil H Ueno J M Manning K Tanizawa K Nishimura K Soda D Ringe B Stoddard G A Petsko 《Biochemistry》1989,28(22):8798-8803
Incubation of pure bacterial D-amino acid transaminase with D-serine or erythro-beta-hydroxy-DL-aspartic acid, which are relatively poor substrates, leads to generation of a new absorbance band at 493 nm that is probably the quinonoid intermediate. The 420-nm absorbance band (due to the pyridoxal phosphate coenzyme) decreases, and the 338-nm absorbance band (due to the pyridoxamine phosphate or some other form of the coenzyme) increases. A negative Cotton effect at 493 nm in the circular dichroism spectra is also generated. Closely related D amino acids do not lead to generation of this new absorption band, which has a half-life of the order of several hours. Treatment of the enzyme with the good substrate D-alanine leads to a small but detectable amount of the same absorbance band. D-Serine but not erythro-beta-hydroxyaspartate leads to inactivation of D-amino acid transaminase, and D-alanine affords partial protection. The results indicate that D-serine is a unique type of inhibitor in which the initial steps of the half-reaction of transamination are so slow that a quinonoid intermediate with a 493-nm absorption band accumulates. A derivative formed from this intermediate inactivates the enzyme. 相似文献