Biosynthesis of isoprenoids in intact cells of Escherichia coli

Abstract

Upon rehydration of lyophilized Escherichia coli cells with phosphate buffer containing [14C]isopentenyl pyrophosphate (IPP), 14C was incorporated into the cells. Radioactivity was found in ubiquinone-8, an unidentified precursor of ubiquinone-8, demethylmenaquinone-8 and phosphate esters of all-trans-octaprenol and cis, trans-polyprenols. On rehydration of the cells with the buffer containing geranyl pyrophosphate or farnesyl pyrophosphate in combination with [14C]IPP, higher radioactivity was incorporated into the above products and some radioactivity was found in free prenols. Fractionation of the 14C-labeled cells by sucrose-density gradient centrifugation before and after recultivation indicated that the size of 14C-labeled cells had changed during the recultivation. This shows that radioactivity of [14C]IPP was incorporated into live cells but not into dead cells. The metabolism of the radioactive products in the recultivated cells was examined. It was found that the unidentified precursor was converted to ubiquinone-8, but demethylmenaquinone-8 was not converted to menaquinone-8. "Lipid intermediates" in peptidoglycan synthesis increased in the logarithmic growth phase and decreased in the stationary phase. In the stationary phase, however, an increase in cis,trans-polyprenyl monophosphates was observed. These observations suggest the operation of the lipid cycle of peptidoglycan synthesis.