Purification of a protein from Nitellopsis obtusa cells and its involvement in the regulation of potential-dependent Ca2+ channels

A protein was isolated from the thermostable protein fraction of N. obtusa cells and purified by hydrophobic chromatography on phenyl-Sepharose and affinity chromatography on melittin-Sepharose. In 15% polyacrylamide gel, the protein has an electrophoretic mobility corresponding to M_r 17,000 in the presence of 1 mM Ca²⁺ and M_r no higher than 19,000 in the presence of 1 mM EGTA. Introduction of the protein isolated to a perfused N. obtusa cell affects the electric parameters of the plasmalemma Ca²⁺ channels. This influence shows up as a change in I_Ca²⁺, as well as an activation of the electrogenous processes in the plasmalemma. The protein produces restoration of I_Ca²⁺ in the Ca²⁺ channels blocked by chlorpromazine. Possible mechanisms of involvement of this protein in regulation of the functional state of potential-dependent Ca²⁺ channels of N. obtusa plasmalemma are assumed.