Detergent solubilization of the respiratory nitrate reductase of Bacillus stearothermophilus

Four detergents (octyl glucoside, zwittergent, Triton X-100, and Nonidet P-40) were examined with regard to their efficiency in solubilizing and retaining the activity of the nitrate reductase of Bacillus stearothermophilus. At a concentration of between 0.4 and 0.6%, the non-ionic detergent octyl glucoside solubilized only 64% of the membrane proteins. However, about 100% of the nitrate reductase activity was recovered in the soluble fraction. In contrast, the zwitterionic detergent 3-(alkyldimethylammonio)-1-propanesulphonate (3-16) solubilized 100% of the membrane proteins, but only 77% of the nitrate reductase activity was recovered. Two other non-ionic detergents, Triton X-100 and Nonidet P-40 also solubilized 100% of the membrane proteins, but there was a dramatic increase in total enzyme activity following solubilization. The enzyme activity was not stable in any of the four detergents for more than 2 days. Nevertheless, octyl glucoside was preferred because of the additional advantage of ammonium sulphate fractionation.