GUANOSINE TETRAPHOSPHATE AND PENTAPHOSPHATE PROMOTE ACCUMULATION OF INORGANIC POLYPHOSPHATE IN ESCHERICHIA-COLI

High levels of guanosine tetraphosphate (ppGpp) and guanosine pentapho sphate (pppGpp), generated in response to amino acid starvation in Esc herichia coli, lead to massive accumulations of inorganic polyphosphat e (polyP). Inasmuch as the activities of the principal enzymes that sy nthesize and degrade polyP fluctuate only slightly, the polyP accumula tion can be attributed to a singular and profound inhibition by pppGpp and/or ppGpp of the hydrolytic breakdown of polyP by exopolyphosphata se, thereby blocking the dynamic turnover of polyP. The K-i values of 10 mu M for pppGpp and 200 mu M for ppGpp are far below the concentrat ions of these nucleotides in nutritionally stressed cells. In the comp lex metabolic network of pppGpp and ppGpp, the greater inhibitory effe ct of pppGpp (compared with ppGpp) leading to the accumulation of poly P, may have some significance in the relative roles played by these re gulatory compounds.