Intermolecular Bonding of the Antibiotic Diumycin

Abstract

The closely related antibiotics diumycin A and B, with monomeric molecular weights of approximately 1800 daltons in ethanol, aggregate in aqueous buffers to form particles with a molecular weight (mol. wt.) of at least 32,000 daltons. The aggregate of diumycin is essentially unaffected by esterification of the acid, acetylation of hydroxyl groups, high ionic strength buffer, or variations in pH from 2.2 to 12.4. These results indicate that salt linkages and hydrogen bonds contribute only slightly to stabilize the aggregate. The aggregate may be disrupted by: (a) the addition of such hydrophobic bond‐breaking agents as buffered aqueous solutions of guanidinium chloride, urea, or formamide; (b) the hydrolytic loss of a lipid side chain (mol. wt. about 400 daltons); or (c) the addition of alcohols. The ability of an alcohol to disrupt the aggregate increases with its hydrocarbon content. From these data, it is concluded that lipid‐lipid hydrophobic interactions are responsible for the self‐association of diumycin. The aggregate is spherical with a mantle of hydrophilic sugars, including glucose and glucosamine, surrounding a tangle of lipid side chains.