Modification of lysine residues of pepsinogen with dicarboxylic anhydrides

Abstract

Porcine pepsinogen was modified chemically with citraconic, maleic and itaconic anhydrides, and the properties of the derivatives were studied as to the nature and extent of the structural changes in the protein. Modification of the zymogen with citraconic and maleic anhydrides was shown to be partially reversible; the citraconyl and maleyl groups were readily removed under mild acidic conditions. At pH 2.0, 77% and 50% of the potential pepsin activity could be recovered on activation of the citraconyl- and maleylpepsinogens. Itaconylpepsinogen regained only 25% of the potential pepsin activity. From optical rotatory dispersion and circular dichroism measurements it was apparent that a conformational change had occurred with all three pepsinogen derivatives as reflected by a decrease of λ c from 228 to 216–222 nm and au increase of the levorotation, [α] 366. The reappearance of potential pepsin activity parallels the change of the optical rotatory properties.