Abstract
Abstract Oxygen exchange reactions in sonically prepared submitochondrial particles show a nearly absolute dependence upon added adenine nucleotides. The orthophosphate ⇌ adenosine triphosphate and the ATP ⇌ HOH exchange reactions, in contrast to the Pi ⇌ HOH exchange, are favored by presence of ADP rather than ATP, are more sensitive to p-mercuribenzoate and to 2,4-dinitrophenol, and require a higher Mg++ concentration. The marked disparities in exchange rates at low ADP concentrations are theoretically incompatible with a reaction scheme involving only one point of entry of water oxygen. The ATP-driven energy-linked reduction, ATPase activity, and a prominent Pi ⇌ HOH exchange will proceed at much lower Mg++ concentrations than required for the ATP ⇌ HOH and Pi ⇌ ATP exchanges. The Pi ⇌ HOH exchange induced by ATP cleavage occurs principally with Pi of the medium. The ATP ⇌ HOH exchange, but not the Pi ⇌ HOH exchange, appears to occur only in association with oxidative phosphorylation. Reactions separate from the phosphorylation reaction of oxidative phosphorylation appear responsible for ATP-driven energy-linked reduction, ATPase activity, and a prominent Pi ⇌ HOH exchange. These and other results are consistent with a mechanism for oxidative phosphorylation in which a high energy compound or state, independent from concomitant oxidation-reduction, drives water formation directly from an oxygen of Pi, resulting in ATP formation by a concerted reaction or with transient metaphosphate formation. Present data do not, however, eliminate an indirect route of oxygen from Pi to water.
Highlights
Oxygen exchange reactions in sonically prepared submitochondrial particles show a nearly absolute dependence upon added adenine nucleotides
One purpose of the present paper is to present results showing a mandatory requirement of adenine nucleotides for exchange reactions as catalyzed by sonically prepared submitochondrial particles
Enzyme Preparations and Assays-Submitochondrial particles were obtained from freshly prepared bovine heart mitochondria by sonic disruption essentially as described by Smith and Hansen
Summary
Enzyme Preparations and Assays-Submitochondrial particles were obtained from freshly prepared bovine heart mitochondria by sonic disruption essentially as described by Smith and Hansen [9]. Bovine heart mitochondria were prepared as described by Sanadi and Fluharty (lo), but with the use of a Westfalia centrifuge, model KDD-605, driven by a Louis Allis l+-horsepower, variable speed drive, for removal of cellular debris. Heavy bovine heart mitochondria were collected and washed by resuspension and centrifugation according to conventional procedures [10]. Thawed particles (10 ml of a suspension containing 11 mg of protein per ml) were put on a Sephadex G-25 column (43 X 80 mm) and eluted with 0.25 M sucrose containing. Sephadex and charcoal treatment did not impair the energylinked reduction ability
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have