Structure of inorganic polyphosphate (polyP). PolyP is a linear, negatively charged polymer of phosphates held together by high-energy phosphoanhydride bonds. Microbial polyP ranges in size from tens of phosphates to thousands of phosphates long [3, 63], while polyP secreted from human platelets and mast cells is shorter and much less heterodisperse — approximately 60 to 100 phosphate units long [7, 8, 15, 34].