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51.
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Mitochondrial and cytoplasmic isozymes of arginine kinase have been identified inDrosophila melanogaster. On the basis of their immunological similarity, parallel dosage responses, and cosegregation of electrophoretic mobility differences, it is concluded that both isozymes are the product of a single gene. The consequences of this in relation to the regulation and evolution of this unusual gene-enzyme system are discussed. It is inferred that the origin of the phosphagen shuttle must predate the divergence of invertebrates and vertebrates. 相似文献
53.
Glutamic acid 553 of Pseudomonas aeruginosa exotoxin A (ETA) was identified earlier as a putative active-site residue by photoaffinity labeling with NAD. Here ETA-E553D, a cloned form of the toxin in which Glu-553 has been replaced by aspartic acid, was purified from Escherichia coli extracts and characterized. Cytotoxicity of the mutant toxin for mouse L-M cells was less than 1/400,000 that of the wild type. The mutation caused a 3200-fold reduction in NAD:elongation factor 2 ADP-ribosyltransferase activity, as estimated by assays with an active fragment derived from the toxin by digestion with thermolysin. NAD glycohydrolase activity was reduced somewhat less, by a factor of 50, and photoaffinity labeling with NAD by a factor of 2. We detected less than 2-fold change in the values of KM for NAD or elongation factor 2 and no change in KD for NAD, as determined by quenching of protein fluorescence. The drastic reduction of ADP-ribosyltransferase activity therefore results primarily from an effect of the mutation on kcat, implying that Glu-553 plays an important and possibly direct role in catalyzing this reaction. The effects of the E553D mutation are similar to those of the E148D mutation in diphtheria toxin, supporting the notion that these two Glu residues perform the same function in their respective toxins. 相似文献
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J R Collier 《Experimental cell research》1975,95(2):254-262
The RNA and DNA content of the normal and lobeless embryo of the Ilyanassa embryo was measured at several stages of embryogenesis. In the lobeless embryo a delay in the net accumulation of RNA and a decrease in the rate of DNA synthesis were observed. It is suggested that the failure of some of the lobe dependent organs to differentiate may be caused by a reduced rate of proliferation of determined embryonic cells. 相似文献
56.
G I Goldberg A Strongin I E Collier L T Genrich B L Marmer 《The Journal of biological chemistry》1992,267(7):4583-4591
Secreted metalloproteases initiating proteolytic degradation of collagens and proteoglycans play a critical role in remodeling of the connective tissue. Activation of the secreted proenzymes and interaction with their specific inhibitors TIMP and TIMP-2 are responsible for regulation of enzyme activity in extracellular space. We have previously demonstrated that 92- and 72-kDa Type IV procollagenases, in contrast to interstitial collagenase (ClI), form specific complexes with TIMP and the related inhibitor TIMP-2, respectively. The physiologic significance of the proenzyme-inhibitor complex and the mechanism of activation of Type IV collagenases remained unclear. Here, we demonstrate that in the absence of TIMP, 92-kDa Type IV procollagenase (92T4Cl) can form a covalent homodimer and a novel complex with ClI. In the presence of TIMP, the formation of a 92T4Cl proenzyme complex with TIMP prevents dimerization, formation of the complex with ClI, and activation of the 92T4Cl proenzyme by stromelysin, a related metalloprotease. The proenzyme homodimer is unable to form a complex with TIMP. All TIMP-free forms of the proenzyme can be activated by stromelysin. The 92T4Cl-ClI complex can be activated to yield a complex active against both gelatin and fibrillar Type I collagen, suggesting a mechanism for cooperative action of two enzymes in reducing collagen fibrils to small peptides under physiologic conditions. 相似文献
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Davis Emma Trant Andrew Hermanutz Luise Way Robert G. Lewkowicz Antoni G. Siegwart Collier Laura Cuerrier Alain Whitaker Darroch 《Ecosystems》2021,24(5):1038-1058
Ecosystems - The eastern Canadian Subarctic and Arctic are experiencing significant environmental change with widespread implications for the people, plants, and animals living there. In this... 相似文献
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Kutralanathan Renganathan Jiayin Gu Mary E. Rayborn John S. Crabb Robert G. Salomon Robert J. Collier Michael A. Kapin Carmelo Romano Joe G. Hollyfield John W. Crabb 《PloS one》2013,8(10)