Biosynthetic pattern of murine toxins in Pasteurella pestis cells and extracts

Abstract

1. 1. The level of the protein toxins A and B within Pasteurella pestis cells is a function of the growth stage of the culture. Cells from midlog phase (27°) have minimal amounts of toxic material. Two generations later (early stationary phase) the toxic content has increased 7-to 10-fold. At this stage, the cells contain toxin amounting to 5–10 % of their total soluble protein. A small increase in toxin content is observed when the cells are grown at 37°. 2. 2. The low toxin content of young cell extracts is apparently not due to lower protein synthesizing capacity, since they are the most active in amino acid incorporation in vitro. Extracts from 37° grown cells on the other hand exhibit low amino acid incorporating activity, presumably due to limiting amounts of factor(s) in the soluble protein fraction. 3. 3. Pulse and pulse-chase experiments indicate that the two proteins are synthesized simultaneously and independently of one another. No interconversion between toxin A (mol. wt. 240 000) and toxin B (mol. wt. 120 000) by dissociation or dimerization, respectively, has been observed in the cells. 4. 4. Since toxic activity has been found associated with the membrane, and cells containing low levels of these proteins are quite fragile, the possibility that they constitute components of the cell envelope is discussed.