The inner membrane of the rat liver mitochondrion as the site of incorporation of radioactively labeled precursors into nucleic acid and protein in vitro

Abstract

The experiments reported in this study confirm the role of the inner membrane of rat liver mitochondria in the incorporation of radioactive amino acids into protein in vitro and extend that role to include the incorporation of nucleic acid precursors. Purified inner membrane preparations, prepared by a digitonin method, were shown to be capable of effecting the energy-dependent incorporation of 14C-leucine into membrane protein. The process was inhibited by puromycin and chloramphenicol but not by cycloheximide. Actinomycin D also inhibited the reaction. The incorporation of 3H-ATP into mitochondrial RNA and 3H-dATP into DNA by these membranes in vitro was found to be dependent on Mg 2+ and partially dependent on the presence of all four ribo- or deoxyribonucleoside triphosphates. The incorporation of both of these precursors was inhibited by actinomycin D. Inner membranes, prepared from mitochondria by osmotic lysis or sonic vibration, were inactive. Furthermore, active inner membrane preparations prepared by the digitonin method and subsequently exposed to water or sonic treatment were also inactivated. These results suggest that the inner membrane of rat liver mitochondria is capable of incorporating precursors of both nucleic acids and proteins and might carry out the reactions leading from mitochondrial DNA → RNA → membrane protein and that a minimal structural organization might be necessary for the process.