Several major roles of Pi ions have been briefly noted (i.e., intracellular phosphate groups for cellular energetics and biochemical molecules as well as for the skeleton and teeth (structures)). Other important functions also exist. For example, in bone tissue phosphates are critical components of hydroxyapa-tite crystals, and they are also considered triggers for mineralization after phosphorylation of type 1 collagen in forming bone. Serum phosphates, HPO= and H2POj, also provide buffering capacity that helps regulate blood pH and also cellular pH.
Considerable cellular regulation occurs through the phosphorylation or dephosphorylation of Pi ions under the control of phosphatase enzymes, including protein kinases. These cell regulatory roles of Pi ions coexist with regulatory functions involving calcium ions, but Pi ions are much more widely distributed within cells and cell organelles than Ca ions.
Insulin affects Pi ions by increasing their intra-cellular uptake, although temporarily, for the prompt phosphorylation of glucose. Insulin may also influence the use of Pi ions when insulin-like growth factor-1 acts to increase tissue growth or other functions. Because of the broad uses of Pi ions in structural components, energetics, nucleic acids, cell regulation, and buffering, there is an overall generalization that these versatile yet critical ions support life.
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