Calcium chloride, anhydrous: Calcium chloride is a commonly used reagent in biochemistry. Calcium plays important roles in many biological processes, including signal transduction, muscle contraction, and maintenance of cell membrane and cell wall stability. Extensive reviews of the experimental measurement of biological calcium have been published. Calcium chloride is used in the preparation and transformation of competent E. coli and in the transfection of eukaryotic cells with either plasmid DNA or high molecular weight genomic DNA. The CaCl2-mediated electroporation of E. coli with the plasmid DNA pBR322 has been studied. A protocol for the concentration of virus vectors that uses CaCl2 has been published. CaCl2 has been used in the stabilization and two-dimensional crystallization of the NADH-ubiquinone oxidoreductase (complex I) from Escherichia coli. The crystallization of porcine pancreatic elastase in the presence of CaCl2 in the presence of sodium citrate reveals binding of calcium in the metal binding site of the protein. The effect of CaCl2 on the total fluorescence in the polymerication of the tubulin-like FtsZ division protein of Escherichia coli has been studied by a multiwell fluorescent assay.