| Abstract: | Ca2+-dependent GTPase activity is found to be present in the rod outer segments of frog retina. GTPase localization in rod outer segments is shown by fractionating the rod outer segment preparation in the sucrose density gradient. The enzyme is readily washed out of cells with isotonic NaCl solution. The Km is 0.6 mM for GTP. The activity is inhibited by 78 +/- 12% with the increase in Ca2+ concentration from 10(-9) to 10(-7) M. GTP hydrolysis is inhibited by the same concentrations of Ca2+ which block the sodium conductivity of the rod outer segment cytoplasmic membrane. |
