LDHk in the retina of diverse vertebrate species: a possible link to the Warburg effect.

LDHk is a cancer-associated lactate dehydrogenase which is also found at high levels in normal mammalian retina. Such retinas share with most cancer tissues a dependence on aerobic glycolysis, leading to high production of lactate. However, retinas of lower vertebrate species are significantly less dependent on aerobic glycolysis. We find that retinas of species less dependent on aerobic glycolysis express significantly lower levels of an LDHk-like activity, less than or equal to the low levels seen in brains. The enzymes from lower species differ from the mammalian retinal enzyme in their pH optima and responsiveness to oxygen; but share a similar degree of inhibition by 5'-5'-dinucleoside tetraphosphates. Therefore, the expression pattern of LDHk in brain and retina of diverse vertebrate species suggests a link with the Warburg effect.