During oxydase reaction spectral characteristics of ceruloplasmin at absorption of copper ions and protein part of the molecule are shown to change. It has been ascertained, that when irradiating ceruloplasmin by UV-light the functioning of intramolecular electron transport chain is broken, the degree of positive cooperativity (a Hill's constant) on substrate decreases. It is supposed, that these changes are caused by disturbance of interdomain interactions in a protein molecule.