INACTIVATION AND DENATURATION OF SOME PROTEINS BY ENZYME-SYSTEM - MYELOPEROXIDASE, CHLORIDE AND HYDROGEN-PEROXIDE

Changes in biological properties of serum albumin, egg white lysozyme, human serum alpha-1 antiproteinase and human leukocyte ribonuclease i n effect of interaction with the enzyme system composed of myeloperoxi dase from human neutrophilic polymorphonuclear leukocytes, Cl- and H2O 2 were investigated. All the studied proteins lost their biological fu nctions and were denaturated, but the amounts of hydrogen peroxide nec essary to produce these effects differed remarkably for each individua l protein. The alpha-1 antiproteinase ability of binding to trypsin wa s abolished upon employing 1.2 mols of H2O2 per mol of alpha-1 antipro teinase. The lysozyme enzymatic activity was abolished when 1.4 mols o f H2O2 per mol of lysozyme were employed. Albumin decreased its bindin g to specific antialbumin antibodies and entirely lost the binding pro perties when 2 mols and about 10 mols of H2O2 per mol of albumin were employed, respectively. On the other hand 18 mols of H2O2 per mol of h uman leukocyte ribonuclease were necessary to inactivate this enzyme. All the mentioned proteins were protected from losing their biological functions by excess of specific aminoacids with affinity to hypochlor ite: Alpha-1 antiproteinase by excess of N-acetylmethionine, lysozyme by N-acetyl-methionine and N-acetyl glyciltryptophane, albumin by N-ac etyl derivatives of methionine, cysteine, tryptophane and lysine, wher eas ribonuclease was protected from denaturation by all above mentione d aminoacid derivatives. None of the studied proteins was protected fr om denaturation by N-acetyl tyrosine, or phenyloalanine.