Antimicrobial Activity of a Natural and a Synthetic Polypeptide.

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Abstract
A synthetic lysine polypeptide composed of 85 lysine residues was compared with a natural tissue peptide consisting of 30% lysine relative to their antiviral and antibacterial activity. The activity of these substances was tested with a system comprising bacteriophage type A and its host Clostridium madisonii McCoy, strain 16. On a wt. basis, the activity of the synthetic peptide was 4 times greater than that of the natural peptide. The fact that the tissue peptide contained 30% lysine seemed to indicate that the activity resides within the lysine portion of the molecule. Additional evidence to support the implication of lysine was obtained from a comparative study on the mode of inactivation of these peptides by desoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Both peptides combined stoichiometrically at pH 6.5 with DNA but not with RNA; it was apparent that both peptides combine with RNA in multiple proportions depending upon the relative concns. of the reactants. In this respect, the similarity between the RNA-peptide interaction and antigen-antibody reactions is pointed out. A mechanism by which the tissue polypeptide could take part in the natural resistance of animals to infection is postulated. It is assumed that the tissue polypeptide is liberated as a result of tissue damage brought about by the host-parasite interaction. The parasite, therefore, is attacked only within the immediate environment of the necrotic tissue. In addition, the tissue peptides form insoluble complexes with the acidic polysaccharides, hyaluronic acid and heparin. It is suggested that such complexes may be involved in fibrinoid formation.
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