The control of pyruvate oxidation in a cell-free rat heart preparation by phosphate acceptors

Effects of proton motive force on the structure and dynamics of bovine cytochrome C oxidase in phospholipid vesicles

A conventional method for reconstituting cytochrome c oxidase (CcO) into phospholipid vesicles (COV) has been modified to permit resonance Raman (RR) analysis in the presence and absence of proton motive force (ΔμH(+)). The COV has an average diameter of 20 nm and contains one CcO molecule within a unified orientation with CuA located outside the COV. The process of generation of ΔμH(+) across the membrane was monitored spectrophotometrically with rhodamine123 dye. The COV exhibits a respiratory control ratio (RCR) value of >30 and is tolerant to RR measurements with 10 mW laser illumination for 60 min at 441.6 nm. Structural perturbations at the heme sites caused by incorporation into vesicles were clarified by spectral comparisons between solubilized CcO and COV. Absorption spectroscopy revealed that the rate of electron transfer from cytochrome c to O2 is reduced significantly more in the presence of ΔμH(+) than in its absence. RR spectroscopic measurements indicate that CcO in COV in the "respiratory-controlled" state adopts a mixed-valence state (heme a(2+) and heme a3(3+)). This study establishes a supramolecular model system for experimentally examining the energy conversion protein machinery in the presence of ΔμH(+).

Quantification of the relative contribution of parallel pathways to signal transfer: application to cellular energy transduction

A simple mathematical formalism designed to quantify the relative contribution of parallel pathways to signal transduction is presented and applied to the regulation of the respiration rate by ATP, ADP and Pi concentrations in response to an increase of energy demand in isolated mitochondria. Theoretical studies were performed by means of the computer model of oxidative phosphorylation developed previously. Many earlier experimental studies have shown that externally-manipulated concentrations of all three metabolites can influence the respiration rate significantly. However, the effect of changes in [ATP], [ADP] and [Pi] that actually take place during an increased energy demand have not been determined in a quantitative way. It was shown in the present paper that [ADP] is the main regulatory factor which stimulates respiration during transition from state 4 to state 3 imposed by an addition of increasing amounts of an artificial ADP-regenerating system. Changes in [ATP] and [Pi] contribute to the respiration rate increase very weakly, and only in the nearest neighbourhood of state 3. Generally, changes in [ADP] are responsible for approx. 90% of the respiration rate increase during the state 4-->state 3 transition, while the remaining approx. 10% is due to changes in [Pi] and [ATP].

RESPIRATORY CONTROL AND DEHYDROGENASE ACTIVITY

A comparative study has been made of the stimulation of respiration by ADP or by 2,4-dinitrophenol in liver mitochondria incubated with different substrates of NAD-dependent enzymes.It has been found that the degree of stimulation of respiration by ADP or by 2,4-dinitrophenol increased with the number of dehydrogenases involved in the oxidation of the substrate. The respiratory stimulation was greater with higher substrate concentrations. This suggests that the hydrogen pressure produced by dehydrogenase activity was, in each case, the factor which determined the degree of respiratory stimulation.When the concentration of substrate decreased, the stimulation of respiration diminished proportionally, and at very low substrate concentrations was depressed, the rate of respiration in the presence of ADP or 2,4-dinitrophenol being lower than in their absence. Such inhibition of respiration could be reduced or even abolished by increasing the concentration of substrate in the medium. Therefore, not only the degree of respiratory response to ADP or to 2,4-dinitrophenol but also its stimulatory or inhibitory character depended upon the dehydrogenase activity.The concentration of ADP or 2,4-dinitrophenol necessary to induce a maximal respiratory stimulation also increased with the number of dehydrogenases involved in the oxidation of the substrate.

Investigations on the mitochondria of the housefly, Musca domestica L. III. Requirements for oxidative phosphorylation

It has been found that mitochondria isolated from the flight muscle of the housefly, Musca domestica, are capable of effecting oxidative phosphorylation. A systematic investigation of the factors which regulate this coupling was undertaken. It was found: 1. The molarity of the isolation medium had considerable influence on the morphology of the mitochondria. These physical alterations were associated with changes in oxidation, phosphorylation, and ATPase activity. 2. In addition to an optimum isolation medium, the normal morphology of the mitochondria needed to be further stabilized by serum albumin. 3. A "latent" ATPase activity in insect mitochondria was demonstrated. An inverse relationship was found between oxidative phosphorylation and ATPase activity. 4. Oxygen consumption and the uptake of phosphate were linear with respect to time. 5. A respiratory substrate was necessary for phosphorylation and for maintenance of spatially organized mitochondria. 6. No differences in oxygen uptake were found in the presence or absence of inorganic phosphate. 7. Magnesium was required for optimal oxidative phosphorylation. Calcium and manganese inhibited both respiration and phosphorylation. 8. The addition of cytochrome c had no effect on either oxygen or phosphate uptake. 9. ATP, ADP, or AMP were capable of participating in oxidative phosphorylation, but the glucose-hexokinase trapping system was necessary. 10. Fluoride inhibited the phosphorylation of AMP, but increased P/O when ATP was used. This stimulation was not due to the inhibition of ATPase. 11. Neither arginine nor creatine was phosphorylated. 12. The addition of other isolated fractions of flight muscle to the mitochondrial system had no appreciable effect on respiration or phosphorylation.