Complex formation between bacitracin peptides and isoprenyl pyrophosphates. The specificity of lipid-peptide interactions.

The technique used previously to observe complex formation between bacitracin, Mg++, and Ca5-isoprenyl pyrophosphate has been employed to measure association constants. The constant for the bacitracin A, Mg++, C55-isoprenyl pyrophosphate complex was lo6 M-I. The binding constants for other bacitracin peptides were lower and correlated with their antibiotic activities. &farnesyl pyrophosphate also formed a complex with K N lo6 M-l but K for C5-isopentenyl pyrophosphate and for inorganic pyrophosphate was much smaller. The metal ion also influenced the strength of the association constant (Zn++ > Cd++ > Mg++). The pH dependency of complex formation indicated that a defined ionization state was required for maximum stability. These data indicate that both hydrophobic and polar interactions are involved in complex formation.