A rapid colorimetric method for the quantitative determination of copper oxidase activity (ceruloplasmin).

LOOD OXIDASES HAVE BEEN DESCRIBED and discussed since 1912 based on tedious, elaborate means for the determination of their activity. The physiologic significance of oxidase activity has been implicitly associated with the blue copper protein of plasma designated as ceruloplasmin (1, 2, 3, 4, 5, 6). There appears to be a need for a simple, rapid procedure for the determination of ceruloplasmin for the diagnostic studies of Wilson’s disease. Methods described heretofore either were not calibrated to ceruloplasmin concentration of the plasma (hence not adequate for studying hepatolenticular disease) or required elaborate instrumentation. Ravin (7) devised a procedure utifizing the optical density produced on the oxidation of para-phenylenediamine by the copper oxidase but the procedure was not calibrated to ceruloplasmin. The method of Abood et al. (4) did not take in levels below normal and so could not be used for diagnostic studies of hepatolenticular disease. Both required one hour’s incubation. Scheinberg and Morell (8) described an enzymatic method that can be calibrated to known amounts of ceruloplasmin that takes into account the ionic strength of the buffer for maximal activity of the enzyme. This method