Abstract
We purified calmodulin to apparent homogeneity from Tora-mame (Phaseolus vulgaris) seeds, one of the Japanese cultivars of the common bean. Electrophoretically, the purified Tora-mame calmodulin migrated faster than bovine brain calmodulin in the presence or absence of Ca2+. The estimated molecular weight of Tora-mame calmodulin was 14, 200 in the presenc of Ca2+ and 18, 200 in the absence of Ca2+. Like other plant calmodulin, Tora-mame calmodulin lacked tryptophan and contained 1 mol each of tyrosine and half cystine per mol of protein. However, Tora-mame calmodulin has fewer acidic amino acid residues than other plant calmodulins did. Rat brain phosphodiesterase (Ca2+-PDE) was stimulated by Tora-mame calmodulin, but the concentration of Tora-mame calmodulin, giving the half-maximal activation of Ca2+-PDE, was higher than that of bovine calmodulin, and the maximal activity of Ca2+-PDE obtained with Tora-mame calmodulin was lower than that obtained with bovine protein. The Ki value of W-7, a calmodulin antagonist, for Tora-mame calmodulin (17 μM) was larger than that for bovine calmodulin (8 μM). These observations suggest that hydrophobic regions of Tora-mame calmodulin exposed by Ca2+-induced conformational changes were slightly different from those of bovine calmodulin.
