The Role of D-Alanine in the Antigenic Specificity of Bacterial Mucopeptides

Mucopeptides extracted from Gram-positive cocci reacted with antisera against the synthetic random polypeptides poly (l-glu42-l-lys28-d-ala30)n and poly (d-glu16-l-lys16-dl-ala68)n. Quantitative precipitin inhibition studies employing a haptenic inhibitor derived from bacterial mucopeptide and synthetic peptides and polypeptides indicated that d-alanine is a critical amino acid in the antigenic determinant responsible for the cross-reactivity. Only copolymers containing d-alanine residues were effective inhibitors of the cross-reactivity. The results of passive hemagglutination studies of appropriately coated erythrocytes and mucopeptide agglutination reactions with antimucopeptide sera and anti-synthetic polypeptide sera indicated that the immunologic relationship between bacterial mucopeptide and the synthetic copolymers of amino acids is predominantly associated with the presence of d-alanine in the determinant grouping.