| Abstract: | The breakdown of guanosine 5'-diphosphate, 3'-diphosphate (ppGpp) into GDP and PPi is catalyzed by a Mn2+-dependent 3'-pyrophosphohydrolase, the translation product of the spoT gene. The escherichia coli enzyme is normally found to be associated with the "crude" ribosome fraction. It is reported here that the guanosine 5'-diphosphate, 3'-diphosphate 3'-pyrophosphohydrolase activity in this fraction is activated by ATP in the presence of a relatively heat-stable, low molecular weight, supernatant factor (BS100). This stimulation is not due to a removal of reaction products such as by the phosphorylation of GDP to GTP or by the hydrolysis of PPi. Hydrolysis of ATP is probably required because neither adenosine 5'-(3-thio)triphosphate nor adenosine 5'-(beta, gamma-imido)triphosphate can substitute for ATP. Levallorphan, a morphine analog, which had been shown to inhibit in vivo ppGpp degradation, inhibits specifically the stimulation of ppGpp hydrolysis by ATP and the supernatant factor. The possible relationship of this system and the in vivo energy-dependent control of ppGpp degradation is discussed. |
