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921.
922.
J M Vanderkooi R Landesberg G W Hayden C S Owen 《European journal of biochemistry》1977,81(2):339-347
The luminescent properties of metal-free, tin(IV) and zinc(II) cytochromes c have been used to characterize the interaction of cytochrome c with mitochondria and cytochrome oxidase. Diminution in the fluorescence yields of tin and zinc cytochrome c occur when these derivates bind to cytochrome oxidase or mitochondria. Based upon spectral overlap and quantum yield, the distance between the porphyrin rings of cytochrome a and cytochrome c is estimated according to Forster theory to be in the neighborhood of 3.5 nm. Measurements of the polarized emission of metal-free 'porphyrin' cytochrome c when bound to oriented layers of cytochrome c oxidase indicate that the porphyrin is bound obliquely to the plane of the oxidase layers with an angle of about 70 degrees C from heme plane to membrane plane. It is proposed that these data have significance for elucidation of electron transfer mechanisms. 相似文献
923.
The affinity label 5'-p-(fluorosulfonyl)benzoyl adenosine modifies rabbit muscle phosphofructokinase to the extent of one group/subunit. Modification appears to occur at a binding site specific for AMP, cyclic AMP, and ADP, i.e. those adenine nucleotides which are activators under conditions where regulatory kinetic behavior is obtained. The consequences of the modification are consistent with the model proposed previously for correlation between the pK of specific ionizable groups, regulatory kinetic behavior, ligand binding, and the reversible cold inactivation of the enzyme (Frieden, C., Gilbert. H. R., and Bock, P. E. (1976) J. Biol. Chem. 251, 5644-5647). Thus, the modification shifts the apparent pK of the essential ionizable groups from 6.9 to 6.4 at 25 degrees C, with the result that regulatory kinetic behavior at pH 6.9 and 25 degrees C is lost. Furthermore, the apparent affinity of a site (other than the active site) for ATP, as measured by ATP-dependent quenching of intrinsic protein fluorescence at pH 6.9 and 25 degrees C, is decreased by the modification. Regulatory kinetic behavior for both substrates is obtained with the modified enzyme at a lower pH, consistent with the downward shift in the pK of the ionizable groups, but sensitivity to cAMP activation is abolished by the modification. The loss of regulatory kinetic behavior upon modification of sulfhydryl groups does not appear to be the same as that due to modification by the affinity label. 相似文献
924.
The glycogen pellet of dog liver extracts contains a phosphorylase phosphatase which has characteristics different from those of the phosphatases extracted from the cytosol. The phosphatase associated with glycogen is characterized by a M, of 51,000, a half maximal inhibition at 0.3 mM ATP (Hill coefficient : 2) and a Ki for Mg2+ of 1 mM. Treatment with urea or mercaptoethanol of the phosphatase associated with glycogen does not influence the activity, the Mr or the half maximal inhibition by ATP, but a decrease of the Hill coefficient for ATP is observed. A similar treatment of the phosphatases extracted from the high speed supernatant results in a decrease of the Mr of the spontaneously active form from 215,000 to 43,000, without an effect on the Ki for ATP (7 micronM), but accompanied by an increase in activity. The ATP-Mg dependent form of the phosphatase from the high speed supernatant (Mr : 138,000 ; Ka for ATP in the presence of 0.1 mM Mg2+ : 0.3 micronM), is denatured by urea or mercaptoethanol. The phosphatase associated with particulate glycogen cannot be found in the supernatant, nor the phosphorylase phosphatases present in the supernatant in the glycogen pellet. When all the glycogen is mobilized (starvation, glucagon) the phosphatase specifically associated with glycogen cannot be found as such in the cytosol. No activation of synthase beta can be detected neither with the phosphatases extracted from the cytosol nor with the enzyme released from the glycogen pellet. 相似文献
925.
R. W. GIBSON D. WHITEHEAD D. J. AUSTIN JANE SIMKINS 《The Annals of applied biology》1976,82(1):151-153
In a field of potatoes, top-roll, which is induced by the aphid Macrosiphum euphorbiae feeding on the leaves, was restricted to two rows of plants which accidentally received no phorate aphicide granules at planting. The photo-synthetic rate per unit leaf area and the ground cover of top-rolled leaves were respectively 50% and 20% less than those of normal plants which may account for the smaller yields of affected plants observed in previous experiments. 相似文献
926.
The use of a tuberculin syringe as a burette has made possible an easy bedside technique for the determination of serum bicarbonate. By combining it with the use of a simple colorimeter, a relatively untrained person can do numerous bicarbonate determinations with a high degree of accuracy. The same technique also lends itself to other colorimetric clinical procedures such as determination of gastric acidity. 相似文献
927.
928.
Of the 1,972 deaths investigated by autopsy at the Los Angeles County Hospital in 1951, 64 were attributed to bronchogenic carcinoma. However, in some of these cases the protocols did not contain sufficient data to substantiate the diagnosis or the tissue specimens were not conclusive evidence. Although the survey left no doubt that the lung was the most common site of primary carcinoma in the series studied, a wider application of the findings is limited by the facts that patients with bronchogenic carcinoma are more likely than others to die in hospitals and that selection of cases for autopsy depends on the interest of the physician and the consent of the patient's survivors. 相似文献
929.
The apparent conductance (Kss, in W.m-2.degrees C-1) of a given region of superficial shell (on the thigh, fat + skin) was determined on four nonsweating and nonshivering subjects, resting and exercising (200 W) in water [water temperature (Tw) 22-23 degrees C] Kss = Hss/(Tsf-Tsk) where Hss is the skin-to-water heat flow directly measured by heat flow transducers and Tsf and Tsk are the temperatures of the subcutaneous fat at a known depth below the skin surface and of the skin surface, respectively. The convective heat flow (qc) through the superficial shell was then estimated as qc = (Tsf - Tsk).(Kss - Kss,min), assuming that at rest Kss was minimal (Kss,min) and resting qc = 0. The duration of immersion was set to allow rectal temperature (Tre) to reach approximately 37 degrees C at the end of rest and approximately 38 degrees C at the end of exercise. Except at the highest Tw used, Kss at the start of exercise was always Kss,min and averaged 51 W.m-2.degrees C-1 (range 33-57 W.m-2.degrees C-1) across subjects, and qc was zero. At the end of exercise at the highest Tw used for each subject, Kss averaged 97 W.m-2.degrees C-1 (range 77-108 W.m-2.degrees C-1) and qc averaged 53% (range 48-61%) of Hss (mean Hss = 233 W.m-2).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
930.
M J Schilstra J W Slot P H van der Meide G Posthuma A F Cremers L Bosch 《FEBS letters》1984,165(2):175-179
The localization of the elongation factor Tu (EF-Tu) in ultrathin cryosections of E. coli cells was determined with the electron microscope using a highly specific immunological labelling technique. EF-Tu is distributed almost homogeneously throughout the cytoplasm. Although it has often been suggested that EF-Tu could be part of a putative prokaryotic cytoskeleton, we did not find any evidence for supramolecular assemblies, such as fibres or filaments, containing a large amount of EF-Tu. EF-Tu was not observed in association with the outer cell membrane and periplasmic space. A topological relationship with the inner membrane is not apparent in our micrographs. In cells in which the EF-Tu level is raised significantly, the protein piles up in discrete cell regions. 相似文献