The energy-dependent degradation of guanosine 5'-diphosphate 3'-diphosphate in Escherichia coli. Lack of correlation with ATP levels in vivo and role of the transmembrane proton gradient

Abstract

Different inhibitors of the energy metabolism have been assayed in Escherichia coli K12 for their ability to increase the level of guanosine 5'-diphosphate 3'-diphosphate (ppGpp) as a consequence of a restriction of its degradation. Inhibitors of the respiration and uncouplers of oxidative phosphorylations had effects similar to carbon-source-induced downshifts while the ATPase inhibitor dicyclohexylcarbodiimide was less efficient. The effects of dicyclohexylcarbodiimide and of the uncoupler carbonylcyanide p-fluoro methoxyphenylhydrazone (FCCP) on ppGpp degradation were compared in a drug-permeable envelope mutant. At concentrations of inhibitors sufficient to deplete the pool of ATP by 50%, only FCCP was able to block ppGpp degradation. Moreover, FCCP also inhibited ppGpp degradation in a ATPase-deficient strain growing on glucose as carbon source while, as expected, it did not change the level of ATP. It is concluded, according to Mitchell's chemiosmotic hypothesis, that, in vivo, the integrity of the transmembrane proton gradient rather than the ATP pool size is a prerequisite for the normal processing of the energy-dependent degradation of ppGpp.