= Mitochondrial oxygen electrode assay
In Respiratory enzymes in oxidative phosphorylation. I. Kinetics of oxygen utilization (1955), <Britton Chance> and <G. R. Williams> examined isolated liver <mitochondria> in isotonic medium with <substrate> and <inorganic phosphate>. A one-millilitre optical <cuvette> held the suspension. A vibrating <platinum> <electrode> lay outside the light path; calibrated <electric current> followed dissolved <oxygen>, with rapid changes recorded by a galvanometer oscillograph. Air-saturated and oxygen-depleted readings checked sensitivity. Their Figure 2 shows <ADP> additions accelerating <oxygen> consumption, followed by return to slow respiration; repeated additions restored acceleration. Figure 4B compares delayed <substrate> addition after <ADP> incubation with the reverse order, supporting little unrelated <ADP> loss in that preparation. These comparisons support coupling to <ADP> utilization. The authors discuss dilution, sensitivity changes and atmospheric <oxygen> entry, which especially biases slow respiration. The readout did not directly measure the <membrane potential> or prove the later <chemiosmosis> mechanism.<Respiratory enzymes in oxidative phosphorylation. I. Kinetics of oxygen utilization by Britton Chance and G. R. Williams>[pp. 383–386, Preparations and Method, Figures 1–2; pp. 387–389, Endogenous Substrate and Figure 4B; Figure 5: rapid recording]{ref}
\Image[/mitochondrial-respiratory-control-electrode.png]
{title=An <oxygen> <electrode> reveals the respiratory response to <ADP>}
{description=Original schematic of an open <cuvette>, vibrating <platinum> <electrode> outside the optical path, and repeated <ADP>-dependent <oxygen> responses. Boxes encode no measured times, slopes or <concentrations>.}
A control can test either the instrument or the biology. Calibrating <electric current> against <oxygen> checks the former; comparing responses before and after an <ADP> addition checks the latter. A valid calibration cannot by itself establish <ATP> formation, and a repeatable biological response cannot by itself fix an instrument's sensitivity.
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