Myeloperoxidase of Human Leukaemic Leucocytes

Abstract

Myeloperoxidase was isolated from leucocytes obtained from the blood of patients suffering from chronic granulocytic leukaemia. The enzyme was purified 850 fold and was homogeneous in ultracentrifuge and free boundary electrophoresis. The molecular weight of the enzyme was found to be about 160,000. The enzyme forms a spectrally characteristic complex with hydrogen peroxide with absorption maximum at 458 mμ. The spectrum of the native enzyme has absorption maxima at 430 and 570 mμ. The reduced enzyme is characterized by a spectrum with absorption maxima at 472 and 637 mμ. The investigated myeloperoxidase catalysed oxidation of amino acids by hydrogen peroxide. Products of the oxidation of amino acids were ammonia, carbon dioxide, and an aldehyde corresponding to the oxidized amino acid. The observed reaction of deamination and decarboxylation is activated by chloride ions. In the presence of the chloride ions the optimum of the reaction is shifted toward the higher pH values. The velocity of the reaction was found to be dependent on the concentration of the amino acid studied. K m values for various amino acids increased in the range 3.4 × 10 −4 to 10 −3 M in proportion to rising hydrophobic properties of the substrates. Taurine was found to be a competitive inhibitor in the examined reaction, and K i values were in the range of 2 to 3 × 10 −4 M, for different amino acids.