Factor C, a regulatory protein of Streptomyces griseus induces release of potassium from the mycelium

External potassium concentration was measured in suspensions of washed living mycelia of Streptomyces strains. An active uptake of K+ by the mycelium was observed from the medium at proper aeration and stirring. The endogenous regulatory protein factor C. in very low concentrations (down to 0.7 ng ml−1), induced in a specific way the release of K+. Changes in the electrolyte composition of the medium had moderate effect on the factor C induced K+ release. Factor C proved to be active in nine different Streptomyces strains. Only S. griseus 45H, the producer of factor C, did not respond. Response to factor C was not affected by chloramphenicol or actinomycin D. The process followed a “slow kinetics” with 3–10 min latency of K+ release. It was assumed that the factor C induced K+ release could be the consequence of a more rapid process realized at the level of existing macromolecules.