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A Cheung J A Engelke C Sanders J W Suttie 《Archives of biochemistry and biophysics》1989,274(2):574-581
The liver microsomal vitamin K-dependent carboxylase catalyzes the post-translational conversion of specific glutamyl to gamma-carboxyglutamyl (Gla) residues in precursor forms of a limited number of proteins. These proteins contain an amino-terminal extension (propeptide) that is presumed to serve as an enzyme recognition site to assure their normal processing. The free, noncovalently bound propeptide has also been shown to stimulate the in vitro activity of this enzyme. This peptide has now been shown to lower the app Km of a low-molecular-weight Glu site substrate while having no influence on the app Km of the other substrates, vitamin KH2, O2, and CO2/HCO3-. Propeptide addition was shown to have no influence on the ratio of the two products of the enzyme, Gla and vitamin K-2,3-epoxide. Stimulation of carboxylase activity by the propeptide from human factor X was observed in a number of rat tissues and in the liver of a number of different species. Stability of the enzyme in crude microsomal preparations was greatly enhanced by the presence of propeptide. These observations are consistent with the hypothesis that this region of the protein substrates for the carboxylase not only serves an enzyme recognition or docking function but also modulates the activity of the enzyme by altering the affinity for one of its substrates. 相似文献
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Effects of tRNA-intron structure on cleavage of precursor tRNAs by RNase P from Saccharomyces cerevisiae. 总被引:11,自引:4,他引:7
RNase P derived from S. cerevisiae nuclei was tested for its ability to cleave a variety of naturally occurring and selectively altered precursor-tRNA molecules to yield matured 5' termini. Precursors were synthesized in vitro in order to test which aspects of substrate structure are crucial to recognition and cleavage by RNase P. Base modifications in the precursor substrates are not required for cleavage by the enzyme, but deletion and substitution mutations affecting any portion of the precursor tertiary structure reduce cleavage. In particular, a number of alterations in the intervening sequence (IVS) reduce the susceptibility of the substrate to cleavage by RNase P. The significance of these results is discussed in reference to the contribution of the IVS to the structure of the precursor-tRNA. 相似文献
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A novel experimental method was developed which allows the determination of the threshold concentration of sucrose by use of a linear sucrose gradient in water. With this method a continuous tasting of the test-liquid is possible. A panel of 15 persons experienced in taste-testing was used. Three gradients of different steepness were applied: 0 to 1.5% (w/w) sucrose in 2 min (I), 3 min (II) and 4 min (III). The results of the new method were compared with those of the standard method (DIN). With gradients I and II we found values which were significantly higher than those of the standard method (I: 0.49% (w/w); II: 0.46% (w/w); DIN: 0.31% (w/w)), whereas with gradient III the same threshold value was found as with the DIN-Method (III: 0.32% (w/w)). 相似文献
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Nonclottable fibrin obtained from partially reduced fibrinogen: characterization and tissue plasminogen activator stimulation. 总被引:1,自引:0,他引:1
Out of 29 disulfide bonds in human fibrinogen, 7 were cleaved during limited reduction under nondenaturing conditions in calcium-free buffer: 2 A alpha 442Cys-A alpha 472Cys and 2 gamma 326Cys-gamma 339Cys intrachain disulfide bonds in the carboxy-terminal ends of the A alpha- and gamma-chains and the symmetrical disulfide bonds at gamma 8Cys, gamma 9Cys, and A alpha 28Cys. We studied the loss of thrombin clottability that followed limited reduction and the increase in the susceptibility of the fibrinogen A alpha 19-A alpha 20 bond to hydrolysis by thrombin. Using differential scanning calorimetry, we show that the extent of unfolding and denaturation of specific domains following limited reduction is small. Heat absorption peaks corresponding to the melting of the major regions of compact structure give high calorimetric enthalpies, as in untreated nonreduced fibrinogen, indicating that substantial regions of native structure are still present in partially reduced fibrinogen. Thrombin releases fibrinopeptide A at an identical rate as in nonreduced fibrinogen while fibrinopeptide B release is slower. Sedimentation velocity studies show that thrombin treatment leads to complex formation; however, gelation does not occur. Amino-terminal analysis indicates that the second thrombin cleavage in the A alpha-chain at A alpha 19-A alpha 20 takes place only after fibrinopeptide A release. Thus, the loss of clottability appears to result from perturbation of carboxy-terminal polymerization sites, probably a consequence of gamma 326Cys-gamma 339Cys intrachain disulfide bond cleavage. The thrombin-treated partially reduced fibrinogen remains soluble in buffered saline and fully expresses at least one epitope, B beta 15-21, unique to fibrin. Furthermore, this nonclottable form accelerates the tissue plasminogen activator dependent conversion of plasminogen to plasmin. 相似文献
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Crandall C. G.; Johnson J. M.; Convertino V. A.; Raven P. B.; Engelke K. A. 《Journal of applied physiology》1994,77(4):1863-1867
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The Duwamish River Floating Wetlands project designed, built, and deployed constructed floating wetlands in the estuary of the urban Duwamish River in Seattle, Washington, during the 2019 and 2020 outmigration seasons for juvenile salmon. Using a “safe-to-fail” methodology and adaptive management strategies, these innovative floating wetland prototypes were custom designed to provide the native plants, invertebrates and slow water habitat that juvenile salmon require during their transition from fresh to salt water, and were monitored for these outcomes. This paper will provide insight into the prototype designs, adaptive management strategies and plant performance, and unique public-private-academic-community partnerships that supported 2 years of design and research. 相似文献
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