ACTIVATION BY A CALCIUM-BINDING PROTEIN OF GUANYLATE-CYCLASE IN TETRAHYMENA-PYRIFORMIS

A Ca2+-binding protein (TCBP), which was isolated from Tetrahymena pyriformis, enhanced about 20-fold particulate-bound guanylate cyclase activity in Tetrahymena cells in the presence of a low concentration of Ca2+, while the adenylate cyclase activity was not increased. The enhancement was eliminated by ethylene glycol-bis (β-aminoethyl ether)-N,N′-tetraacetic acid. The enzyme activity was not stimulated by rabbit skeletal muscle troponin-C, the Ca2+-binding component of troponin, or other some proteins. In the presence of TCBP, stimulating effect of calcium ion on the enzyme activity was observed within the range of pCa 6.0 to 4.6, and was immediate and reversible. © 1979.