LDHk, an unusual oxygen-sensitive lactate dehydrogenase expressed in human cancer.

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Abstract
An unusual isozyme of lactate dehydrogenase (LDH; L-lactate:NAD+ oxidoreductase, EC 1.1.1.27), LDHk, has been described in cells transformed by the Kirsten murine sarcoma virus (KiMSV). This isozyme appears to contain 1 or more subunits encoded by the transforming gene of KiMSV and is readily distinguished from other isozymes of LDH. Specifically, it is more basic than other LDH isozymes, has an apparent subunit structure (35,000)4 (22,000)1, is essentially inactive if assayed under a normal atmosphere and is strongly inhibited by GTP and various related compounds. Human cancer and normal tissue controls were examined for expression of an activity like LDHk. In 11 of 16 human carcinomas, LDHk activity was increased 10- to 500-fold over the level seen in adjoining nontumor tissue. Other LDH isozymes were increased by only 2- to 5-fold.