[Lysis of Micrococcus lysodeikticus protoplasts by gramicidin S derivatives]

Gramicidin S derivatives with the substituted amino groups of ornithines (carbamoylgramicidin and diacetylgramicidin) possess nearly the same level of the lytic activity when acting on Micrococcus lysodeikticus protoplasts in a 1 M sucrose solution as the original antibiotic. The lytic activity of gramicidin S and these derivatives considerably increases in a solution of sucrose in phosphate buffer. The dependence of the lytic activity of gramicidin on its concentration is of a complex character: two "peaks" of activity and a region of "nonlyzing" concentrations. The lytic activity of gramicidin derivatives with substituted amino groups directly depends on the concentration. When gramicidin S acts upon the intact cells of M. lysodeikticus, it impair with the permeability of their membranes and causes a loss of compounds absorbing at 260 nm; the derivatives with the substituted amino groups change the permeability of the cellular membranes only to a slight extent.