Studies on the Chemical Nature of a Normal Plasma Factor Which Suppresses Variation of Brucella Abortus

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Abstract
Summary: Normal bovine serum, and plasma globulin Fractions II and III-0, which produce a selective suppression of the establishment of non-smooth variants in broth cultures of Brucella abortus, were subjected to dialysis, pH changes, heat treatment, and to the action of proteolytic enzymes, polynucleotidases, urea, guanidine, formaldehyde, and other chemical reagents. The effects of such treatment upon the selective activity were investigated. The results indicate that the selective activity is referable to non-dialyzable protein components, and that bovine plasma contains two distinct substances which possess this selective activity. One, a γ-globulin protein, is stable at low pH, and is inactivated by 6M guanidine hydrochloride. The other appears to be a lipoprotein, associated with a β-globulin fraction; it is very unstable at low pH, resistant to 6M guanidine, and destroyed by freezing to −25 C in the presence of ether.