INCORPORATION OF [P-32] ORTHOPHOSPHATE INTO INORGANIC POLYPHOSPHATES BY HUMAN GRANULOCYTES AND OTHER HUMAN CELL-TYPES

When human peripheral blood granulocytes were metabolically labeled at 37-degrees-C with [P-32] orthophosphate, inorganic polyphosphates bec ame preferentially radiolabeled. Incorporation of radiolabel into the polymer appeared to be ATP-independent. [P-32]Polyphosphate was identi fied by its (i) characteristic lability to acid hydrolysis, (ii) insol ubility in barium acetate (pH 4.5), (iii) conversion to [P-32]trimetap hosphate, (iv) hydrolysis to [P-32]orthophosphate by an exopolyphospha tase (Saccharomyces cerevisiae scPPX1), and (v) conversion to a ''phos phate ladder''which co-migrated on a polyacrylamide gel with a synthet ic phosphate ladder. Also, indirect evidence suggested that the [P-32] polyphosphate was strongly, noncovalently associated with another unkn own molecule. Particulate fractions (13,000 x g) from lysates of human granulocytes, skin fibroblasts, HL-60 and SK-N-SH cells, all demonstr ated radiolabeling of polyphosphate when incubated at 37-degrees-C wit h [P-32] orthophosphate.