Abstract
Abstract With suitable submitochondrial particles from the heart, the rate of the inorganic phosphate ⇄ HOH exchange during substrate oxidation in the absence of ADP is less than 1/1000 of the rate in the presence of ADP. The concentration dependence of the exchange on ADP shows simple saturation behavior with an apparent Km of 0.32 mm. For net oxidative phosphorylation under similar conditions, but with a hexokinase-glucose trap present, the apparent Km for ADP is 0.58 mm. The ADP analogue, adenosine methylene diphosphonate, is not detectably phosphorylated, does not stimulate the Pi ⇄ HOH exchange in the absence of ADP, and does not inhibit the exchange in the presence of ADP. The submitochondrial particles show the presence of an oligomycin and a 2,4-dinitrophenol-sensitive ADP ⇄ ATP exchange. These results are consistent with the interpretation that the Pi ⇄ HOH exchange results from dynamic reversal of ATP formation at the catalytic site, and that in the phosphorylation reaction the first covalent compound formed from Pi or ADP is ATP.
Highlights
A DPNH-regenerating system was present to make conditions closely analogous to those used in a comparison experiment in which net ATP formation was measured
The results show that within the range of experimental error the velocity of the Pi Z+ HOH exchange shows a hyperbolic dependence on ADP concentration quite analogous to a simple
The results show that the ADP-stimulated exchange is obliterated by oligomycin, the small ADP-independent l*O incorporation into Pi is not affected by the inhibitor
Summary
MatcriaZs-82Pi from various commercialsourceswaspurified before use as described elsewhere[16]. Adenosine 5’-methylene diphosphonate was purchased from Miles Laboratories, Inc.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
