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 in effect of interaction with the enzyme system composed of myeloperoxidase from human neutrophilic polymorphonuclear leukocytes, Cl- and H2O2 were investigated. All the studied proteins lost their biological functions and were denaturated, but the amounts of hydrogen peroxide necessary to produce these effects differed remarkably for each individual protein. The alpha-1 antiproteinase ability of binding to trypsin was abolished upon employing 1.2 mols of H2O2 per mol of alpha-1 antiproteinase. The lysozyme enzymatic activity was abolished when 1.4 mols of H2O2 per mol of lysozyme were employed. Albumin decreased its binding to specific antialbumin antibodies and entirely lost the binding properties 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 human leukocyte ribonuclease were necessary to inactivate this enzyme. All the mentioned proteins were protected from losing their biological functions by excess of specific amino acids with affinity to hypochlorite: Alpha-1 antiproteinase by excess of N-acetylmethionine, lysozyme by N-acetylmethionine and N-acetyl glycyltryptophane, albumin by N-acetyl derivatives of methionine, cysteine, tryptophane and lysine, whereas ribonuclease was protected from denaturation by all above mentioned amino acid derivatives. None of the studied proteins was protected from denaturation by N-acetyl tyrosine, or phenylalanine.