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941.
Proalbumin differs from serum albumin in containing a leading hexapeptide segment, Arg-Gly-Val-Phe-Arg-Arg. This propeptide is removed in the Golgi complex immediately prior to secretion of the albumin, but its fate and possible functions are unknown. We have tested for the presence of the propeptide and its immediate catabolic products in rat liver and plasma and have studied both the disappearance of 3H-propeptide after intravenous injection and the breakdown of synthetic propeptide by rat liver cell components and plasma in vitro. We found no detectable propeptide or its two pentapeptide derivatives in rat liver or plasma at a sensitivity of less than 1 microM. Injected 3H-propeptide was completely cleared from blood within 2 min. No binding of free propeptide to serum albumin was observed. Liver cell fractions as well as blood plasma degraded added propeptide, with the highest activity being observed in smooth microsomes, the Golgi-enriched fraction, and plasma membrane. These preparations chiefly removed the terminal arginine residues, whereas enzymes in the cytosol degraded the peptide completely to amino acids. The activity in plasma resided largely in an alpha-globulin with molecular mass of about 280,000 Da which appears to be carboxypeptidase N. We conclude that the liberated propeptide is quickly broken down within the liver cell and does not accumulate in an amount sufficient to exert feedback or other effects on albumin synthesis. 相似文献
942.
Breathing strategy of the adult horse (Equus caballus) at rest 总被引:1,自引:0,他引:1
To investigate the mechanism underlying the polyphasic airflow pattern of the equine species, we recorded airflow, tidal volum, rib cage and abdominal motion, and the sequence of activation of the diaphragm, intercostal, and abdominal muscles during quiet breathing in nine adult horses standing at rest. In addition, esophageal, abdominal, and transdiaphragmatic pressures were simultaneously recorded using balloon-tipped catheters. Analysis of tidal flow-volume loops showed that, unlike humans, the horse at rest breathes around, rather than from, the relaxed volume of the respiratory system (Vrx). Analysis of the pattern of electromyographic activities and changes in generated pressures during the breathing cycle indicate that the first part of expiration is passive, as in humans, with deflation toward Vrx, but subsequent abdominal activity is responsible for a second phase of expiration: active deflation to below Vrx. From this end-expiratory volume, passive inflation occurs toward Vrx, followed by a second phase of inspiration: active inflation to above Vrx, brought about by inspiratory muscle contraction. Under these conditions the abdominal muscles appear to share the principal pumping duties with the diaphragm. Adoption of this breathing strategy by the horse may relate to its peculiar thoracoabdominal anatomic arrangement and to its very low passive chest wall compliance. We conclude that there is a passive and active phase to both inspiration and expiration due to the coordinated action of the respiratory pump muscles responsible for the resting adult horse's biphasic inspiratory and expiratory airflow pattern. This unique breathing pattern perhaps represents a strategy of minimizing the high elastic work of breathing in this species, at least at resting breathing frequencies. 相似文献
943.
D T Sharpe A H Roberts T L Barclay W A Dickson J A Settle D J Crockett M G Mossad 《BMJ (Clinical research ed.)》1985,291(6500):945-948
On 11 May 1985 the main stand of Bradford City Football Club caught fire. Within four minutes the stand was alight from end to end. Fifty three people were burnt to death and about 250 injured; 83 required admission to hospital, and 55 of these were treated by primary excision of their burns and skin grafting. In such disasters the help of staff from other hospitals and areas is essential. Patients should be assessed to see whether they have burns that will ultimately be fatal; if they have they should not be sent to regional burns units, where they would take up beds that could be used for patients with treatable burns. All districts should ensure that their plans for accidents in which burns injuries predominate are adequate. 相似文献
944.
G Iu Miterev G F Burova M S Puzhitskaia S V Danilevich T I Bulycheva 《Biulleten' eksperimental'no? biologii i meditsiny》1987,103(6):710-712
Two hybridomas secreting mouse cytotoxic monoclonal antibodies to in vivo and in vitro activated human T-lymphocyte and neutrophil surface membrane antigenic determinants have been produced. One of these monoclonal antibodies (Ta/H-2) appeared to be also specifically reactive to blast cells in the majority of non-T-non-B and T acute lymphoblastic leukemia patients. 相似文献
945.
T J Beeler 《The Journal of biological chemistry》1980,255(19):9156-9161
The rate of calcium uptake by sarcoplasmic reticulum vesicles isolated from rabbit skeletal muscle was stimulated by inside-negative membrane potential generated by K+ gradients in the presence of valinomycin. The increase in the calcium transport rate was accompanied by a proportional increase in the rate of calcium-dependent ATP hydrolysis, without significant change in the steady state level of the phosphorylated enzyme intermediate. Changes in the sarcoplasmic reticulum membrane potential during calcium transport were monitored with the optical probe, 3,3'-diethylthiadicarbocyanine. The decrease in the absorbance of 3,3'-diethylthiadicarbocyanine at 660 nm following generation of inside-negative membrane potential was reversed during ATP-induced calcium uptake. These observations support an electrogenic mechanism for the transport of calcium by the sarcoplasmic reticulum. 相似文献
946.
947.
D. C. Coleman R. V. Anderson C. V. Cole E. T. Elliott L. Woods M. K. Campion 《Microbial ecology》1977,4(4):373-380
Flows of biomass and respiratory carbon were studied in a series of propylene-oxide sterilized soil microcosms. One-half of the microcosms received three pulsed additions of 200 ppm glucose-carbon to mimic rhizosphere carbon inputs. Biotic variables were: bacteria (Pseudomonas) alone, or amoebae (Acanthamoeba) and nematodes (Mesodiplogaster) singly, or both combined in the presence of bacteria.Over the 24-day experiment, respiration was significantly higher in the microcosms containing the bacterial grazers. Biomass accumulation by amoebae was significantly higher than that by nematodes. The nematodes respired up to 30-fold more CO2 per unit biomass than did amoebae. Similar amounts of carbon flowed into both respiratory and biomass carbon in microcosms with fauna, compared with the bacteria-alone microcosms. However, partitioning of available carbon by the microfauna varied considerably, with little biomass production and relatively more CO2-C produced in the nematode-containing microcosms. The amoebae, in contrast, allocated more carbon to tissue production (about 40% assimilation efficiency) and correspondingly less to CO2. 相似文献
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