Kinetic studies of the reaction of papain with succinic anhydride demonstrate the reactivity of 10 amino groups, two of which are easily deacylated giving a stable succinylpapain with 3 free amino groups one of which is the free amino group of the terminal isoleucin. This modified enzyme has the tenfold solubility of papain between pH 5,9 - 9 and is a little more sensible to temperature than papain. Kinetic parameters of succinylpapain with N-Benzoyl-ʟ-arginine ethylester are: Km app =1,2 x 10-2 ᴍ( papain: 1,8 x 10-2 M) κcat=505 min-1 (papain: 475 min-1) at pH 6,2 and 37°C. The activity with the anionic substrate casein was 120 ± 10%, with the cationic protamine was 200 ± 20% of the activity of papain.Nitration of 17 ± 1 tyrosines of succinylpapain with tetranitromethane has only a limited effect on the activity of the enzyme. The kinetics of this reaction suggests the existence of three groups of tyrosines with different reactivity. The reaction of papain with tetranitromethane gives only insoluble, cross-linked products.Three of five present tryptophanes of papain and succinylpapain are oxidized by N-bromosuccinimide in the native state; in 8 ᴍ urea all residues are accessible. The esterase- and proteolytic activity of the oxidized enzyme decrease to less than 50% of controls while with benzoyl-ᴅ, ʟ-arginine-p-nitro-anilide there was observed an increased activity of about 250%. The stability of the enzyme drops considerably after oxidation of five tryptophane residues. Function and reactivity of the modified amino acids are discussed with regard to the results of the x-ray analysis of the enzyme
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