Uncoupling agents: arsenical analogues of pyrophosphate and their compounds.

Arsenate does this because the enzyme accepts it as orthophosphate, but the first product breaks down because of the instability of esters and anhydrides of arsenate (cf. Braunstein, 1931). This use of arsenate is limited because most of the biochemical reactions that liberate orthophosphate, in contrast with those that liberate pyrophosphate, are not freely reversible. Arsenical analogues of pyrophosphate may therefore be expected to undergo similar reactions with a wide range of enzymes. They should change a reaction of the type: NTP+ X-H -+ N-O-PO(0H)-X + PPj (where N is a nucleoside) to