SKP2 and mitochondrial disease: By contrast, lactate levels measured in whole worm population tissue homogenates reflect the sum of intracellular and extracellular lactate levels, an important difference that we postulate underlies the observed reduction in the overall lactate level in fbxl-1(ok3741) worms, where tissue lactate used as a metabolic substrate may potentially be greater in the mitochondrial disease worms relative to controls.