γ-Radiolysis of Trypsin, Chymotrypsin, and Chymotrypsinogen When Associated with DNA

Abstract

Complexes between DNA and chymotrypsin, chymotrypsinogen, and trypsin were irradiated as aqueous solutions. Marked protection was afforded the enzymes in the associations, and this was not attributable to radical scavenging by the nucleic acid component. Enzymatic activity was lost in a manner unique to each preparation of complex and to each of several substrates employed, which suggests that the precise interaction between the nucleic acid and protein components is critical in affecting the nature of the damage sustained by the protein. This was confirmed by amino acid analysis. The character of the destruction of amino acid residues after radiolysis of the complexes suggests that random attack by the products from the irradiation of water occurs on the proteins. The active sites are apparently protected either by the geometry of the DNA/ protein complex or by the nucleic acid acting to divert the free radical attack. (auth)