Myeloperoxidase is a component of the microbicidal network of polymorphonuclear leukocytes. The enzyme is a tetramer consisting of two heavy and two light subunits. A large proportion of humans demonstrate genetic deficiences in the production of myeloperoxidase. As a first step in analyzing these deficiencies 1n more detail, we have isolated cDNA clones for myeloperoxidase from an expression library of the HL-60 human promyelocytic leukemia cell line.Two overlapping plasmids(pMP02 and pMP062) were identified as myeloperoxidase cDNA clones based on the detection with myeloperoxidase antiserum of 1)70 kDa protein expressed 1n pMP02-conta1n1ng bacteria and 2) a 75 kDa polypeptide produced by hybridization selection and translation using pMP062 and HL-60 RNA. Formal identification of the clones was made by matching the predicted amino add sequences with the amino terminal sequences of the heavy and light sub-units. Both subunits are encoded by one mRNA in the following order: pre-pro-sequences -- light subunit -- heavy subunit.The molecular weight of the predicted primary translation product 1s 83.7 kDa. Northern blots reveal two size classes of hybridizing RNAs(approximately 3.0-3.3 and 3.5-4.0 kilobases) whose expression is restricted to cells of the granulocytic lineage and parallels the changes in enzymatic activity observed during differentiation.
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