New copper binding components of blood plasma (992.1)

Abstract

It has been assumed for some time that the main Cu‐containing proteins in blood plasma are ceruloplasmin (Cp), albumin and transcuprein/a2‐macroglobulin, Cp being the main ferroxidase (Fx) implicated in mediating efflux of iron from certain cells. Recent studies in our laboratory suggest the picture is much more complex, and that other known and unknown factors containing Cu are still to be identified. We had previously shown in mice that knocking out Cp only knocked down plasma Fx activity by half. We now have evidence that knocking out hephaestin (Hp) a membrane‐tethered Cp‐homologue reduces plasma Fx activity and a peak in the Cu profile obtained by size exclusion chromatography (SEC), indicating that solubilized Hp may be entering the circulation. Also, a patient with twice normal level of plasma Cu but Cp protein in the normal range had twice normal levels of Fx activity, suggesting that ratios of holo to apo‐Cp were elevated or that another Fx increased in response to the contraceptives. Use of the anticoagulant, EDTA, to collect plasma had a dramatic effect on SEC Cu profiles, moving a large proportion of Cu in larger components (but not Cp) to one of low molecular weight normally present in trace amounts, which is not Cu‐EDTA or metallothionein. We conclude that the proportions of plasma Cu associated with Cp and Fxs can vary widely and speculate that a copper peptide normally attached to other proteins is dislodged by EDTA.Grant Funding Source: HHMI 52007532