The sequence of ppGpp and pppGpp in the reaction scheme for magic spot synthesis.

The kinetics of ppGpp (guanosine 5'-diphosphate, 3'-diphosphate) ahd pppGpp (guanosine 5'-triphosphate, 3'-diphosphate) synthesis, at the onset of amino acid starvation, and of their decay after inhibiting synthesis, were analysed in Escherichia coli. The pentaphosphate, but not ppGpp, is the first product of the stringent response to amino acid starvation. The pentaphosphate is rapidly converted with first order kinetics (t 1/2 = 6 s) to ppGpp which is broken down less rapidly (t 1/2 = 20 s).