The acid-base transformations of the gramicidin S molecule in water were studied. The protonization constants of the antibiotic amino group were calculated by the data of the potentiometric titration and the antibiotic distribution in the system of chloroform-water: K1 1.55 X 10(10), K2 1.38 X 10(6), the logarithm of the distribution coefficient of gramicidin S in the system of chloroform-water (1:1) lg alpha G 4.10. By the same data the constants of water solubility of gramicidin S base (1.02 X 10(7) mol/l), gramicidin S monohydrate (1.06 X 10(-4) mol/l) and gramicidin S dihydrochloride (2.08 X 10(-4) mol/l) were calculated.
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