In contrast to the types of transfers in Chapters 3–8, that involve attack of cosubstrate nucleophiles, including water, on phosphoric anhydrides and phosphate esters that result in transfer of electrophilic phosphoryl groups, inorganic phosphate can instead be coaxed by certain enzymes into action as an oxyanion nucleophile. For inorganic phosphate monoanions or dianions to behave as nucleophiles there must be cosubstrate electrophiles to attack. In large measure phosphorylases use inorganic phosphate to attack glycosyl (most often glucosyl) C1-oxocarbenium ions as the requisite electrophilic cosubstrates. Classically, glycogen phosphorylase uses Pi to mobilize glucosyl end units from glycogen polymers by release of glucose-alpha-1-phosphate molecules. In a sense the transmembrane F-type ATP synthases, responsible for >90% of the daily inventory of ATP synthesized and utilized by organisms, offer a phosphorus-centric version of a phosphate oxygen nucleophile attacking an electrophilic phosphorus: in this case the Pi phosphorus is actually the electrophile and a beta oxyanion of ADP is the nucleophile.