INORGANIC POLYPHOSPHATE IN MAMMALIAN-CELLS AND TISSUES

Inorganic polyphosphate (polyP), a linear polymer of hundreds of ortho phosphate (P-i) residues linked by high-energy, phosphoanhydride bonds , has been identified and measured in a variety of mammalian cell line s and tissues by unambiguous enzyme methods, Subpicomole amounts of po lyP (0.5 pmol/100 mu g of protein) were determined by its conversion t o ATP by Escherichia coli polyphosphate kinase and, alternatively, to P-i by Saccharomyces cerevisiae exopolyphosphatase, Levels of 25 to 12 0 mu M (in terms of P-i residues), in chains 50 to 800 residues long, were found in rodent tissues (brain, heart, kidneys, liver, and lungs) and in subcellular fractions (nuclei, mitochondria, plasma membranes, and microsomes). PolyP in brain was predominantly near 800 residues a nd found at similar levels pre- and postnatally, Conversion of P-i int o polyP by cell lines of fibroblasts, T-cells, kidney, and adrenal cel ls attained levels in excess of 10 pmol per mg of cell protein per h. Synthesis of polyP from P-i in the medium bypasses intracellular P-i a nd ATP pools suggesting the direct involvement of membrane component(s ). In confluent PC12 (adrenal pheochromocytoma) cells, polyP turnover was virtually complete in an hour, whereas in fibroblasts there was li ttle turnover in four hours, The ubiquity of polyP and variations in i ts size, location, and metabolism are indicative of a multiplicity of functions for this polymer in mammalian systems.