Lactate and pyruvate concentrations in exercised ischemic canine muscle: relationship of tissue substrate level to lactate dehydrogenase isozyme pattern.

Publisher Website
Google Scholar
Abstract
Lactate and pyruvate concentrations in canine skeletal muscle stimulated anaerobically to exhaustion attain the peak but not the inhibitory portion of the curve relating lactate dehydrogenase (LDH) activity to substrate concentration. The LDH activities of whole homogenates of canine cardiac and skeletal muscle behave similarly at 25[degree]C in the presence of increasing concentrations of substrate. Differences with isolated purified LDH-1 and LDH-5 at the unphysiologic temperature of 25 [degree]C diminish at physiologic temperatures where the extent of substrate inhibition is less. In contracting human uterus at term, tumor tissues, and HeLa and KB-9 cells, substrate concentrations do not attain levels that inhibit LDH isozymes. These observations are incompatible with the theory that LDH-5 is the predominant isozyme in "anaerobic" environments because substrate concentrations are so high that they inhibit LDH-1, but not LDH-5.