Inhibition of Lobster‐Muscle Arginine Kinase by Homologous Antibodies and Study of an Antibody Population Directed against a Tyrosine‐Containing Antigenic Structure

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Abstract
The effect of highly inhibitory rabbit antibodies on the enzymic activity of lobster [Homarus vulgaris] muscle arginine kinase was studied. Total inhibition was obtained at a 30-fold molar excess of antibody. The guanidine substrate L-arginine did not protect the enzyme from subsequent inhibition by its antibodies. The metal-nucleotide substrate Mg-ATP, or the substrate analog Mg-AMP, protected about 50% enzyme activity, the extent of the protection being irrespective of the presence or absence of L-arginine and of the value of the molar antibody/antigen ratio. An antibody population directed against the antigenic determinant containing the essential tyrosine residue of the enzyme was isolated by affinity chromatography. No inhibitory activity was found in that fraction. Most of the inhibitory activity was in the remaining antibody populations. The combination of tyrosine-containing antigenic determinant with its specific antibodies is not responsible for the inactivation of the enzyme upon antibody binding; the environment of the nucleotide substrate binding site could be implicated in the inhibitory action.