Characterization of the Calcium‐Binding Contractile Protein Centrin from Tetraselmis striata (Pleurastrophyceae)

ABSTRACT. Centrin is a major protein of the contactile striated flagellar roots of the green alga Tetraselmis striata. We present a newly modified procedure for the preparation of centrin in sufficient quantity and purity to allow for detailed biochemical characterization. We establish that centrin purified by differential solubility, followed by phenyl‐Sepharose and DEAE‐Sephacel chromatography is identical with the protein extracted directly from striated flagellar roots with regard to molecular weight, isoelectric point, and calcium‐dependent behavior in SDS‐PAGE. We also compare the biochemical properties of purified centrin with calmodulin isolated from Tetraselmis and calmodulin isolated from mammalian brain. Centrin can be fully distinguished from either algal or mammalian calmodulin on the basis of molecular weight, isoelectric point, calcium‐dependent behavior in SDS‐PAGE, proteolytic peptide maps, amino acid composition, ability to activate bovine brain phosphodiesterase, and reactivity with specific antibodies.