Ion accumulation in bacterial systems: I. Isolation of two particulate fractions participating in silicon metabolism, from Proteus mirabilis cell-free extracts

Two particulate fractions, both derived from the bacterial membrane system, have been isolated from Proteus mirabilis cell-free extracts after ultrasonic disrupture of the cells and several centrifugation steps. Both fractions are very similar with respect to their flavin and cytochrome composition, oxidize NADH and succinate, and represent mainly the respiratory chain of the organism. The two fractions differ in their attitude toward silicate: The first fraction—precipitating between 25,000 and 100,000 g—is capable of accumulating silicate during substrate oxidation, accompanied by extra oxygen consumption, and represents a respiration-linked ion accumulating system. The second fraction, which is obtained between 100,000 and 250,000 g, catalyze the reduction of silicate, presumably due to a lack of binding capacity, according to the small size of these particles.