= Joe M. McCord
{c}
\b[Joe M. McCord] helped identify the enzymatic activity called <superoxide dismutase>. His 1981 first-person research recollection describes how an unexpected inhibition of <cytochrome c> reduction led to a different explanation of oxygen-dependent <enzyme> chemistry.<Citation Classic commentary on Superoxide dismutase by Joe M. McCord>[Page1, account of the1968 experiments and1969 isolation/assay paper]{ref}
The system contained <xanthine oxidase>, oxygen and a <cytochrome c> reporter. McCord initially sought direct binding between <xanthine oxidase> and an inhibitory <protein>. The eventual explanation involved freely diffusible <superoxide>: its competing removal could inhibit the reporter without the proposed binding. Preparations of other <proteins> contained a small amount of the catalytically active contaminant.<Citation Classic commentary on Superoxide dismutase by Joe M. McCord>[Page1, unsuccessful binding hypothesis, solution intermediate and contaminating dismutase]{ref}
The <superoxide dismutase> reaction is a <disproportionation>:
$$
2\,\mathrm{O_2^{\bullet-}}+2\,\mathrm{H^+}
\longrightarrow\mathrm{O_2}+\mathrm{H_2O_2}.
$$
In an original <stoichiometry> example, reaction of 40 <superoxide> equivalents produces 20 oxygen and 20 <hydrogen peroxide> equivalents. Decreasing the <superoxide> signal therefore need not mean producing only water. Likewise, a smaller <cytochrome c> reporter signal can reflect a competing reaction rather than less activity of the source enzyme. This is why a reporter's measured change must be connected to a reaction mechanism before interpreting an <enzyme assay>.
\Image[https://pathwaysbio.com/wp-content/uploads/MCC.png?_t=1714589269]
{title=Joe McCord, portrait identified in the Pathways Bioscience scientific-team profile}
{height=300}
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