A Functional Tyrosyl Residue in Arginine Kinase, Studied by Nitration with Tetranitromethane

The nitration of arginine kinase from lobster muscle (Homarus vulgaris) with tetranitromethane has been studied after reversible blocking of its thiol groups. Experimental procedure for nitration of one essential tyrosyl residue is described. The introduction of one mononitrotyrosine per mole of arginine kinase results in a total loss of activity. Reduction to the aminotyrosine derivative does not restore enzymic activity. The mononitrotyrosyl arginine kinase is unable to bind its nucleotides or guanidine substrates as judged by differential spectrophotometry. An important conformational change occurring on nitration of one reactive tyrosine residue is demonstrated by means of optical rotatory dispersion measurements and immunodiffusion.