LDHk, the lactate dehydrogenase associated with transformation by the Kirsten sarcoma virus: a re-evaluation.

A lactate dehydrogenase isozyme designated "LDHk" has recently been described in cells transformed by the Kirsten murine sarcoma virus. Several unusual properties were felt to distinguish this LDH isozyme from previously described LDH isozymes. These properties include cathodic electrophoretic migration in acrylamide gels using an imidazole/borate buffer system, inhibition of activity by oxygen and GTP, and stimulation of activity by cyanide. However, this report demonstrates that the muscle-type mammalian LDH isozyme, LDH 5, also exhibits these unusual properties when it is isolated and detected by the same methods previously used to demonstrate LDHk. The unusual properties attributed to LDHk are not intrinsic properties of the enzyme itself but rather result from the methods employed to demonstrate LDHk activity. Numerous similarities exist between LDH 5 and LDHk including electrophoretic mobility, substrate requirements, similar Michaelis constants for lactate, pyruvate, NAD, and NADH, and identical tissue distribution, indicating that LDHk represents mammalian LDH 5.