Summary
Quantitative platelet 12-lipoxygenase (12-LOX) deficiency has been reported in some
patients with myeloproliferative disorders (MPD). We report here for the first time
a novel qualitative abnormality of the 12-LOX enzyme of platelets from a patient with
essential thrombocythemia. The anti-12-LOX immunoprecipitates from the patient’s platelet
homogenates showed a deficiency of 12-LOX activity, but contained normal amount of
12-LOX protein. There was no difference in subcellular localization of the enzyme
between the patient’s platelets and normal ones. This 12-LOX protein lacking its enzyme
activity showed slightly larger electrophoretic mobility than normal one, suggesting
a molecular abnormality of the enzyme. However, we could not detect any genetic mutation
causing such abnormalities in all exons of 12-LOX gene by sequencing the patient’s
PCR-amplified DNA. Thus, our results indicate that the deficient activity of this
abnormal 12-LOX protein is probably due to a posttranslational modification, and the
possibility that platelets of some MPD patients have qualitative abnormality of the
12-LOX enzyme besides quantitative one.
