Inhibition of serum naphthylamidases by atopic allergens

Abstract

Human serum hydrolyses the 2-naphthylamides of -lysine and -arginine. The enzymatic activity of the serum naphthylamidases is inhibited by atopic allergens and by protein-sugar conjugates carrying 1-deoxy-2-ketose residues attached to the -amino groups of lysine residues in their peptide moieties. The inhibiting capacity of these substances was found to be directly related to the number of sugar-linked lysine residues in the molecular framework. The sensitivity spectrum of the serum naphthylamidases towards other modifiers indicates these enzymes to be identical with, or closely related to serum leucine aminopeptidase. No difference was detected in the behavioural pattern of these enzymes from the sera of allergic patients with regard to inhibition by allergens. It is suggested that the inhibitory action of atopic allergens may, as a side-effect, impair the ability of allergic individuals to inactivate lysyl-bradykinin (kallidin) generated in response to the initial allergen-reagin interaction.