Increased Synthesis of Lactate Dehydrogenase "H" Subunit by a Malignant Tumor

In a patient with a rapidly growing malignant teratoma in the anterior mediastinum, the only biochemical abnormality detected at first was an abnormally high serum lactate dehydrogenase (EC 1.1.1.27) activity, almost 50% of the activity being present in lactate dehydrogenase isoenzyme-1 (LD1). At the time of death, the total lactate dehydrogenase activity had increased still further, 77% of it being in the LD1 fraction. Both the tumor and its hepatic metastases were shown to have a supranormally active LD1 fraction. These patterns appear to be attributable to an increased synthesis of the "H" subunit by the tumor.