Dr. Heinonen reviews and critically evaluates the scientific literature on the biological role of inorganic pyrophosphate (PPi ) published from 1940 to the end of 1999. He describes and classifies all known biochemical reactions that produce Ppi; describes and evaluates all published methods used in biological Ppi; and compiles and critically evaluates information on the concentration of PPi (with the conclusion that, contrary to common belief, PPi...