Abstract
A colistin-like active substance was found in the cell extract of colistin-producing organism, Bacillus colistinus. This substance was designated colistin X and differed from known colistin on bioautograms and on gel filtration on Sephadex G-100 where it appeared in a protein fraction. Binding of 14C-labeled colistin with the cellular protein of the organism was noted in low colistin ratios, such as approximately 260 u/mg protein, by incorporating radioactivity into the protein fraction in gel filtration. The paper radiogram of the binding reaction mixture gave a radioactive spot corresponding to colistin X. In contrast, in high colistin ratios the cellular protein used was partially degraded by reaction with colistin.
From these results, it was assumed that the intracellular colistin X was a binding complex of colistin and cellular protein.
