EFFECT OF PHOTOOXIDATION ON HUMAN CAERULOPLASMIN

Human caeruloplasmin showed a rapid loss of p‐phenylene‐diamine oxidase activity when subjected to photooxidation in the presence of methylene blue. Major conformational changes did not occur. The kinetic characteristics of the loss of phenylene‐diamine oxidase activity were comparable to those of the destruction of histidine residues, and the relative extent of the two processes indicated a one‐to‐one correspondence between them. Copper was lost at a slower rate than that of destruction of histidine residues. It is suggested that the site responsible for the oxidase activity of caeruloplasmin may contain an essential histidine residue and that, although histidine residues may also be involved in copper binding, they are not exclusive copper ligands. Copyright © 1969, Wiley Blackwell. All rights reserved