ABSTRACT
The specific modification of tyrosyl residues in proteins has provided considerable information regarding the participation of these residues in the catalytic processes of enzymes as well as specific binding processes of proteins. There are a number of reagents which may result in the modification of tyrosyl residues. The reaction of chymotrypsinogen A with diazotized arsanilic acid has been investigated. Diazotization of arsanilic acid is accomplished by treatment of p-arsanilic acid with nitrous acid. Iodination is somewhat infrequently used for the modification of tyrosyl residues in protein. The reaction is still of considerable value since the process of the radiolabeling of proteins with either of the iodine radioisotopes primarily involves the modification of tyrosine residues in proteins. The extent of modification of tyrosyl residues by tetranitromethane in proteins can be assessed by either the spectophotometric means or by amino acid analysis.
