Iodination of Muscle Fructose Diphosphate Aldolase

The effect of iodine incorporation on the catalytic activities of rabbit muscle d -fructose 1,6-diphosphate aldolase has been examined. The inactivation that takes place concomitant with binding of only a few atoms of iodine per molecule of aldolase is not accompanied by a gross conformational change in the enzyme. It is concluded that iodination of a specific tyrosyl residue or residues of muscle aldolase is responsible for the marked inactivation. A significant portion of the iodine incorporated is associated with the COOH-terminal tyrosyl residues. Two COOH-terminal tryptic peptides have been isolated with the use of 125 I as the marker, and the amino acid compositions of these peptides have been determined.