Quick guide: ATP synthase

denotes the soluble catalytic headgroup where ATP synthesis and hydrolysis occur, and F o is the ion-translocating membrane domain (see Figure). What is it? An enzyme that uses energy from the transmembrane proton electrochemical gradient, generated by oxidative metabolism or photosynthesis, to produce ATP from ADP and P i. The enzyme can also act in reverse, hydrolysing ATP and pumping H + or Na +. Where is it found? In energy-transducing membranes such as the plasma membrane of bacteria and blue–green algae, the inner membrane of mitochondria and the thylakoid membrane of chloroplasts. Hence, they play a fundamental role throughout nature producing the 'universal energy exchange currency' ATP. It first came to prominence… … in the early 1960s when lollipop-like structures were observed on mitochondrial membranes by electron microscopy. The large soluble domain, F 1 , can be detached and was shown to hydrolyse ATP. Later, ATP hydrolysis and synthesis were shown to be coupled to H + translocation through the complex, consistent with Peter Mitchell's chemiosmotic theory. Its first heyday was… … probably 1994 when the crystal structure of the F 1 headgroup was solved by John E. Walker and colleagues. The structure supported the 'binding change mechanism' proposed by Paul D. Boyer — a sequential change in the binding affinities of the alternating catalytic sites in F 1 to promote tight substrate binding and product release during catalysis — and provided a structural basis for a rotary mechanism of catalysis. Walker and Boyer were awarded the Nobel Prize for Chemistry in 1997. Its second coming will be when the entire complex of F o is solved. How does it work? As a molecular motor. There is good evidence that H + movement occurs at the interface between the fixed subunit a and the mobile subunit c oligomeric ring (see figure). The oligomeric c ring is attached to the central stalk and forms a spindle within the complex that turns at several thousand revolutions per minute. The asymmetrical central stalk interacts with the subunits of the surrounding catalytic headgroup and couples events at the catalytic sites with H + movement. Other speculated functions include… … maintenance of an electrochemical gradient necessary for secondary transport and, in some bacteria, cytoplasmic pH, by working in reverse, hydrolysing ATP and pumping H +. Does it have any relatives? Yes, the vacuolar ATPase (V 1 V o) and archaeal ATPase (A 1 A …