Chemical modification of amino acid residues in human plasminogen

The chemical modification of human plasminogen (HPg) was studied with 1-ethyl-3-(3-dimethylamino-propyl) carbodiimide(EDC), N-acetylimidazole(NAI), 1,2-cyclohexanedione(CHD), chloramine T(Ch-T) and N-bromosuccinimide(NBS) as modifying reagents at its carboxyl group, tyrosine, arginine, methionine and tryptophan residues, respectively. The results indicate that tyrosine and arginine residues are not essential for HPg activity, while carboxyl groups, methionine and tryptophan residues are important for the activity of HPg. The Keech and Farrant's kinetic analysis reveals that one tryptophan residue, one methionine residue and two carboxyl groups are essential for HPg activity.