As the team responsible for Duce et al. 2010, Cell 142: 857, we are puzzled by these published findings.
We have reproduced the ferroxidase activity of APP in the transferrin assay using both in-house purified APP, as well as a recombinant full length APP-Fc fusion construct that is commercially available (http://www.creativebiomar...).
Concerning the assertion that we were measuring auto-oxidation, in our original publication, Duce et al. 2010, Cell 142: 857, we blanked our transferrin loading absorbance values on background auto-oxidation of iron in the absence of enzyme. In doing so we followed the published protocols of Bakker & Boyer 1986, J. Biol. CHem., 261: 13182, as we stated.
We plan to publish this further validation and optimization of the APP ferroxidase activity in a peer reviewed journal as soon as practicable. We will make a point of providing the background oxidation curves to show that this reaction is relatively minor compared to the APP-catalyzed iron oxidation, which resembles ceruloplasmin. We note that this may also be a suitable subject for the new PLOS ONE Reproducibility Initiative.