The general formula, proposed earlier for the natural streptothricins E, D, C, B, A and for the biosynthetic streptothricin X was shown to be valid.
1. The presence of a common moiety in streptothricins F, E, D, C, B and A was demonstrated by isolation of N-guan-streptolidyl gulosaminide from preparations of all these antibiotics.
2. It was shown that streptothricins D, C, B, A and X contain unbranched peptide chains, in which residues of β-lysine are linked by their ε-amino groups, whereas β-amino groups are free.