(First of Two Parts) THE part played by phagocytes in defense against invading pathogens has been recognized since 1883. In that year, Metschnikoff, a Russian zoologist, reported that foreign particles injected into metazoans (in Metschnikoff's experiments, starfish larvae) were taken up by a population of "wandering mesodermal cells" that resided in interstitial tissues.1 He postulated a crucial role in host defense for these wandering cells, which he named "phagocytes." Since Metschnikoff's discovery, hundreds of scientists studying dozens of species have reported thousands of studies on these cells, perhaps the most widely recognized of which are those of the eminent English . . .

Oxygen-dependent microbial killing by phagocytes (second of two parts).

Oxidatively modified lipoproteins have been implicated in atherogenesis, but the mechanisms that promote oxidation in vivo have not been identified. Myeloperoxidase, a heme protein secreted by activated macrophages, generates reactive intermediates that oxidize lipoproteins in vitro. To explore the potential role of myeloperoxidase in the development of atherosclerosis, we determined whether the enzyme was present in surgically excised human vascular tissue. In detergent extracts of atherosclerotic arteries subjected to Western blotting, a rabbit polyclonal antibody monospecific for myeloperoxidase detected a 56-kD protein, the predicted molecular mass of the heavy subunit. Both the immunoreactive protein and authentic myeloperoxidase bound to a lectin-affinity column; after elution with methyl mannoside their apparent molecular masses were indistinguishable by nondenaturing size-exclusion chromatography. Peroxidase activity in detergent extracts of atherosclerotic lesions likewise bound to a lectin column and eluted with methyl mannoside. Moreover, eluted peroxidase generated the cytotoxic oxidant hypochlorous acid (HOCl), indicating that enzymatically active myeloperoxidase was present in lesions. Patterns of immunostaining of arterial tissue with antihuman myeloperoxidase antibodies were similar to those produced by an antimacrophage antibody, and were especially prominent in the shoulder region of transitional lesions. Intense foci of myeloperoxidase immunostaining also appeared adjacent to cholesterol clefts in lipid-rich regions of advanced atherosclerotic lesions. These findings identify myeloperoxidase as a component of human vascular lesions. Because this heme protein can generate reactive species that damage lipids and proteins, myeloperoxidase may contribute to atherogenesis by catalyzing oxidative reactions in the vascular wall.

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Myeloperoxidase, a catalyst for lipoprotein oxidation, is expressed in human atherosclerotic lesions.

Protein Carbonyl Measurement by a Sensitive ELISA Method

Activated phagocytes generate the potent oxidant hypochlorite (HOCl) via the release of the enzyme myeloperoxidase and hydrogen peroxide. HOCl is known to react with a number of biological targets including proteins, DNA, lipids and cholesterol. Proteins are likely to be major targets for reaction with HOCl within a cell due to their abundance and high reactivity with HOCl. This review summarizes information on the rate of reaction of HOCl with proteins, the nature of the intermediates formed, the mechanisms involved in protein oxidation and the products of these reactions. The predicted targets for reaction with HOCl from kinetic modeling studies and the consequences of HOCl-induced protein oxidation are also discussed.

Hypochlorite-induced oxidation of amino acids, peptides and proteins.

Dityrosine, a specific marker of oxidation, is synthesized by the myeloperoxidase-hydrogen peroxide system of human neutrophils and macrophages.

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. Km 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 Ki values were in the range of 2 to 3 × 10−4 M, for different amino acids.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1968.tb00246.x

T. Stelmaszyńska

Papers

Myeloperoxidase of Human Leukaemic Leucocytes Oxidation of Amino Acids in the Presence of Hydrogen Peroxide