1m although the s erythraeus protein has a homology

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1M Although the S. erythraeus protein has a homology with eukaryotic CaM, it has been pointed out that the protein has an even higher homology with a group of eukaryotic sarcoplasmic Ca 2+ -binding proteins 165 (see Section V.D). The search for a prokaryotic CaM analogue continues, and the prospect of success has been improved after recent reports of a 21-amino-acid-Iong polypeptide from an E. coli heat-shock protein 166 that shows the typical structural features of CaM-binding domains in other eukaryotic proteins. 167 Table 3.6 Aligned EF-hand sequences for the prokaryotic and human calmodulins. Ligands 3 5 7 9 12 S. erythraeus protein I D F D G N G A L E R A D II G V G S D G S L T E E Q III D K N A D G Q I N A D E IV D T N G N G E L S L D E Human calmodulin I D K D G D G T I T T K E II D A D G N G T I D F P E III D K D G N G y I S A A E IV D I D G D G Q V N y E E
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IX. APPENDIXES 161 Summary The role of Ca 2 + ions in the regulation of biological activities of procaryotic organisms is still largely unsettled. Over the last decade, however, evidence has gradually accumulated that calcium ions are involved in diverse bacterial activ- ities, such as chemotaxis and substrate transport, sporulation, initiation of DNA replication, phospholipid synthesis, and protein phosphorylation. 168 An impor- tant landmark is the recent demonstration that the intracellular Ca 2 + concentra- tion in E. coli is tightly regulated to about 100 nM, a level similar to that typical of resting eukaryotic cells. 169 Furthermore, increasing numbers of calcium-bind- ing proteins, some of which also have putative EF-hand Ca 2 + sites character- istic of the calmodulin superfamily of intracellular regulatory proteins, have been isolated in bacteria. 168 IX. APPENDIXES A. Definition of Biochemical Terms Antiport Basal lateral membrane Cytosol Electrogenic Endocytosis Endoplasmic reticulum (ER) Epithelial cells Erythrocytes Eukaryotic cells A transport protein that carries two ions or molecules in opposite directions across a membrane. The membrane in intestinal epithelial cells that is located on the base of the cells, opposite the microvilli that face the intestinal lumen. The unstructured portion of the interior of a cell-the cell nucleus excluded-in which the organelles are bathed. A biological process driven by electric field gradients. The process by which eukaryotic cells take up solutes and/or particles by enclosure in a por- tion of the plasma membrane to (temporarily) form cytoplasmic vesicles. Sheets of folded membranes, within the cyto- plasm of eukaryotic cells, that are the sites for protein synthesis and transport. Cells that form the surface layer of most, if not all, body cavities (blood vessels, intestine, urinary bladder, mouth, etc.). Red-blood corpuscles.
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