Effects of rifampicin on RNA and protein synthesis in isolated rat liver mitochondria

Abstract

Isolated rat liver mitochondria incorporated [ 3h]utp in an essentially linear fashion for at least 60 min in the presence and absence of exogenous ribonucleoside triphosphates. Preincubation of isolated mitochondria with rifampicin at 0° in the absence of ribonucleoside triphosphates produced a consistent inhibition of [ 3h]utp incorporation at 30° that ranged up to 75 per cent and was independent of preincubation time with rifampicin or the length of the assay period. Incorporation of [ 3H]UMP into mitochondria prepared in the presence of the proteolytic enzyme Nagarse was similarly inhibited by rifampicin. When mitochondria prepared in the presence of Nagarse were preincubated with rifampicin, incorporation of [ 3h]utp was inhibited by approximately 75 per cent within 2 min, while [ 3H] leucine incorporation continued in a linear fashion for 4–5 min before decreasing with first-order kinetics. These data demonstrate that rifampicin primarily affects RNA synthesis in mitochondria, and leads secondarily to an inhibition of protein synthesis. A 75 per cent inhibition of mitochondrial RNA synthesis resulting in a 45 per cent inhibition of mitochondrial protein synthesis permits an estimate of 3.3 mm as the half-life of mitochondrial RNA serving a messenger function. It is hypothesized that this rapidly turning-over mitochondrial RNA which is closely linked to protein synthesis serves a regulatory role in oxidative phosphorylation.