The preparation and properties of mortality enhancing peptide fractions derived from Pseudomonas pseudomallei are described. The mortality of mice, inoculated intraperitoneally with this species, was proportional to the dosage of the fractions, also administered intraperitoneally, over a range of 3 to 30 μg. In the absence of infection, the preparations were nonlethal at a dosage of at least 1000 μg. At 50 μg/mouse, the LD50 of the infecting strain was lowered approximately 1000-fold. The fractions consisted of peptides of varying weight which were, however, similar in amino acid composition, solubility and spectral properties. These properties, in conjunction with others pertaining to biologic activity, suggested that the mortality enhancing peptides were derived from a common protein or similar proteins. A biologically active protein residue, resembling the fractions in certain properties, was demonstrated. The fractions and residue together comprised more than 0.6% of the dry weight of the organism. A crude lipid fraction of the organism also possessed mortality enhancing properties.

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This work was sponsored by the Office of Naval Research, U. S. Navy, and the U. S. Army Chemical Corps, Fort Detrick, Frederick, Maryland, under a contract between the Office of Naval Research and the Regents of the University of California.

Opinions expressed in this report are not to be construed as reflecting the views of the Navy Department or of the naval service at large (Article 1252, U. S. Navy Regulations, 1948). Reproduction in whole or in part is permitted for any purpose of the United States Government.

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