Substrate specificity of caeruloplasmin. Phenylalkylamine substrates

Several phenylalkylamines have been examined as substrates for the copper-containing oxidase caeruloplasmin and it has been shown that the compounds most readily oxidized by this enzyme are those which contain a 3,4-dioxygenation pattern in the aromatic ring. Of these two oxygen atoms, one must be present as a free hydroxy group; the other may be either a hydroxy or methoxy group. A primary amino group may be substituted for one of these oxygen functions without loss of substrate activity. Monophenols are poor substrates for caeruloplasmin. Although the alkylamine side chain is essential for high substrate activity the distance between the basic group of the side chain and the aromatic nucleus is not critical, the higher homologues of dopamine being very good substrates for this enzyme. Monosubstitution at the α-carbon atom of the side chain has relatively little effect on substrate activity but disubstitution at this point markedly reduces substrate activity.