Identification of the C‐1‐Phosphate‐Binding Arginine Residue of Rabbit‐Muscle Aldolase

The arginine‐specific reagent 1,2‐cyclohexanedione reacts selectively with the arginine residue of the C‐1‐phosphate‐binding site of aldolase and inactivates the enzyme. The labeled peptide isolated from tryptic digests of inactivated aldolase was found to correspond to the sequence Leu‐43 to Arg‐56, the residue modified by cyclohexanedione being Arg‐55. This peptide was absent from digests of aldolase treated in the same way but protected from inactivation by the presence of substrate, thus correlating modification of Arg‐55 with loss of activity. Selective isolation of the peptide containing the modified arginine residue was effected by chemisorption chromatography on boric acid gel, a procedure exploiting the specific interaction of matrix‐bound boric acid groups with vicinal m‐hxdroxyl groups of cyclohexanedione‐modified arginine side chains.