The influence of detergents on the availability of pertussis toxin substrates.

Overview

Pertussis toxin-dependent ADP-ribosylation of rat heart and human mononuclear leukocyte membranes was found to be markedly enhanced in the presence of detergents. The order of potency for this effect of detergents was Triton X-100 approximately Lubrol PX greater than digitonin much greater than cholate greater than 3-[(3-cholamidopropyl)dimethylammonia]propanesulfonic acid. Exposure of membranes to increasing concentrations of detergents increased the proportion of pertussis toxin substrate demonstrable in the supernatant fraction whereas the substrate remaining in the pellet fraction demonstrated a complicated relationship with the concentration of detergent. In complementary experiments, it was found that immunochemical detection of G proteins in the pellet fraction from suspensions previously incubated with a maximal concentration of detergent revealed a reduced presence of G proteins with a concomitant increase in the concentration of G proteins in the supernatant fraction; this situation was not observed at submaximal concentrations of detergent during the preincubation of myocardial membranes. The results suggest that the detergent-mediated enhancement of pertussis toxin's action to ADP-ribosylate susceptible G proteins is a complicated process that includes concentration-dependent creation of conditions favorable to the actions of the toxin as well as solubilization of the substrates for the toxin.