Inactivation of transferrin iron binding capacity by the neutrophil myeloperoxidase system
Human serum apotransferrin was exposed to the isolated myeloperoxidase-H2O2-halide system or to phorbol ester-activated human neutrophils. Such treatment resulted in a marked loss in transferrin iron binding capacity as well as concomitant iodination of transferrin. Each component of the cell-free system (myeloperoxidase, H2O2, iodide) or neutrophil system (neutrophils, phorbol ester, iodide) was required in order to observe these changes. In the cell-free system, the H2O2 requirement was fulfilled by either reagent H2O2 or the peroxide-generating system glucose oxidase plus glucose. Both loss of iron binding capacity and transferrin iodination by either the myeloperoxidase system or activated neutrophils were blocked by azide or catalase. The isolated peroxidase system had an acidic pH optimum, whereas the intact cell system was more efficient at neutral pH. The kinetics of changes in iron binding capacity and iodination closely paralleled one another, exhibiting t1/2 values of less than 1 min for the myeloperoxidase-H2O2 system, 3-4 min for the myeloperoxidase-glucose oxidase system, and 8 min for the neutrophil system. That the occupied binding site is protected from the myeloperoxidase system was suggested by (1) a failure to mobilize iron from iron-loaded transferrin, (2) an inverse correlation between initial iron saturation and myeloperoxidase-mediated loss of iron binding capacity, and (3) decreased myeloperoxidase-mediated iodination of iron-loaded versus apotransferrin. Since as little as 1 atom of iodide bound per molecule of transferrin was associated with substantial losses in iron binding capacity, there appears to be a high specificity of myeloperoxidase-catalyzed iodination for residues at or near the iron binding sites. Amino acid analysis of iodinated transferrin (approximately 2 atoms/molecule) demonstrated that iodotyrosine was the predominant iodinated species.
- Research Organization:
- Veterans Administration Medical Center, Iowa City, IA (USA)
- OSTI ID:
- 5872707
- Journal Information:
- J. Biol. Chem.; (United States), Journal Name: J. Biol. Chem.; (United States) Vol. 264:16; ISSN JBCHA
- Country of Publication:
- United States
- Language:
- English
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560300* -- Chemicals Metabolism & Toxicology
59 BASIC BIOLOGICAL SCIENCES
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
AMINO ACID SEQUENCE
ANIMALS
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL EFFECTS
BIOLOGICAL MATERIALS
BLOOD
BLOOD CELLS
BODY FLUIDS
CARCINOGENS
CATALASE
CATALYSIS
CHEMICAL REACTIONS
DOGS
ELEMENTS
ENZYMES
ESTERS
GLOBULINS
GLOBULINS-BETA
HALOGENATION
IODINATION
IODINE ISOTOPES
IRON
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LEUKOCYTES
MAMMALS
MAN
MATERIALS
MEMBRANE PROTEINS
METALLOPROTEINS
METALS
MOLECULAR STRUCTURE
NEUTROPHILS
ORGANIC COMPOUNDS
OXIDOREDUCTASES
PEROXIDASES
PHORBOL ESTERS
PRIMATES
PROTEINS
REACTION KINETICS
RECEPTORS
TRACER TECHNIQUES
TRANSFERRIN
TRANSITION ELEMENTS
VERTEBRATES