Biochemical comparison of myeloperoxidase of leukemic myeloblasts and normal neutrophilic granulocytes.

Myeloperoxidases were purified from leukemic myeloblasts (Mbl-MPO) and from normal neutrophilic granulocytes (Gra-MPO) and were compared with each other biochemically. Gel filtration studies showed that the molecular weights (Mr) of Mbl-MPO and Gra-MPO were about 70,000 and 130,000, respectively, so that the former is almost one-half the molecular size of the latter. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis with 2-mercaptoethanol, both MPOs split into two major subunits, heavy and light peptide chains. However, each of these chains of Mbl-MPO seemed to be smaller than that of Gra-MPO, Mr 58,000 versus Mr 62,000 for the heavy chain and Mr 12,000 versus Mr 15,000 for the light chain. On the other hand, another band of Mr 34,000 also appeared in Mbl-MPO under nonreducing conditions and in both MPOs after being boiled. The size of this band was not different in the two MPOs, but the ratio of this band to the others was much higher in Mbl-MPO. The activity of Mbl-MPO could be demonstrated in the heavy chain of Mr 58,000, using a blotting method, and was found to be less heat stable than that of Gra-MPO. These findings indicate that Mbl-MPO may represent an incomplete, unstable half-enzyme form of Gra-MPO.