Marked activation of benzo[a]pyrene to protein-binding forms in the presence of unsaturated fatty acids and heme-compounds.

In vitro activation of benzo[a]pyrene to protein-binding forms was investigated with the following two systems: (1) various fractions of human and rat blood had a potential of activating benzo[a]pyrene to forms binding to proteins in the presence of linoleic or arachidonic acid. Red blood cells activated much more benzo[a]pyrene than platelets or lymphocytes. Variation in the individual activity of the respective cell types and the relative activity between cells from different individual donors was observed; and (2) more prominent activation of benzo[a]pyrene was observed with a simplified system, in which a combination of unsaturated fatty acid, i.e., linoleic or arachidonic acid, and heme-compounds resulted in activation of benzo[a]pyrene. Although the binding of benzo[a]pyrene to bovine serum albumin did increase with incubation time, an initial rapid reaction within the first few minutes after addition of the substrates was followed by very much reduced rates of binding thereafter. Hematin and hemin could be utilized for the activation of benzo[a]pyrene, but biliverdin, hematoporphyrin and protoporphyrin IX could not. The present results suggest a possible role for unsaturated fatty acids and heme-compounds in the activation of benzo[a]pyrene in vivo.