Arsenic and its metabolites are primarily excreted in the urine.
9.1 and 9.2 Photosynthesis and ATP - 12 cards
Recent experiments (Wantanbe, 2010) using immobilized ATPase and magnetic tweezers have addressed the timing of substrate binding and product release when the enzyme is run in reverse (ATP hydrolysis). On rotation of the gamma subunit, the three binding sites change properties. In hydrolysis, ATP binds to the open site, and helps promote the 120 degree rotation. In the next step, ATP is hydrolyzed. In final step, products dissociate. Pi dissociation occurs last from the third site. Hence each of the 3 beta binding sites have different roles. One binds substrate, one performs catalysis, and third releases products. Assuming the synthesis pathway is the reverse of the ATPase reaction, the final release of Pi in ATP cleavage predicts that Pi binds first in the synthetic direction. This would preclude the binding of ATP next which is critical since its concentration during synthesis can be 10x higher than that of ADP. As Pi is bound first, only ADP, not ATP can bind next.
participating not only in ATP synthesis but ..
The actual amino acids involved in the mechanism of ATP synthesis/hydrolysis are still not clearly defined but Glu 190 on the beta subunit clearly acts as a general base. The figure below shows bound ADP and the proximity of Glu 188. Ala 158 is thought to move towards the active site after a conformational change, with the nonpolar methyl side chain displacing an adjacent water molecule which could leave as a product of ATP synthesis.