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A reaction involving iron as an intermediary electron carrier for the coupling of electron transfer from an endogenous substrate to ferroxidase-I has been proposed.

The enzymic nature of the reacti on has been established and studies with iron chelating agents have demonstrated the involvement of Fe(III). The kinetic parameters of ferroxidase-11 with Fe (lll) were found to be quite similar to those previously established for Fe(Il). The participation by the copper associated with ferroxi dase-11 was ascertained by use of the copper chelating agent, diethyl -di thio-carbamate .

A variety of substances normally found in blood were surveyed as possible candidates for the endogenous substrate but none were oxidized by ferroxidase-II in a coupled reaction with Fe(lll). Complete loss of the Fe(lll)-initiated oxidase activity was observed when ferroxidase-11 was treated with phosphol ipase C and passed over a column of Agarose A-5m.

This procedure removes the bound lipid from ferroxidase-lI and the loss of activity observed suggested that the endogenous substrate was a lipid or was dissolved in the lipid matrix of the enzyme. Attempts to reconstitute this activity with lipid extracts of ferroxidase-11 were unsuccessful.

The endogenous substrate responsible for the Fe(Ill)-initiated reaction was not definitely identified; however, significant progress towards its characterization was made.

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