Localization of L-lactate dehydrogenase in mitochondria

Ambiquitous behavior of rabbit liver lactate dehydrogenase

Rabbit liver mitochondrial fraction shows lactate dehydrogenase activity. The enzyme can be released from particles by increasing the pH and the ionic strength of the medium. There is a narrow range of pH (6.8-7.4) and ionic strength (20-50 mM NaCl) in which the solubilization sharply increases. It has been shown that divalent anions (SO4(2-) and cations (Mg2+, Ca2+) are highly effective specific solubilizing agents. NADH (1.5 mM) and ATP (1.0 mM) were effective in solubilizing 50% of the enzyme bound, whereas the same concentrations of the analogs NAD+ and ADP had little effect. Cytosolic lactate dehydrogenase bound to the mitochondrial fraction and a saturation of particles by enzyme was observed in all experiments performed. The in vitro binding requires a short period of incubation between the enzyme and particles and the binding is independent of the temperature in the 0-37 degrees C range. Binding was prevented by 0.15 M NaCl. The bound enzyme is approximately 20% less active than the soluble one. The results described give support to the proposal that rabbit liver lactate dehydrogenase has an ambiquitous behavior, like other glycolytic enzymes, which have not a fixed intracellular localization.

Lactate dehydrogenase in rat mitochondria

Small but persistent amounts of L-lactate dehydrogenase (LDH) activity were found in mitochondrial preparations isolated from rat heart, kidney, liver, and lymphocytes. Brain mitochondrial preparations were also isolated, but the results were inconclusive. A variety of cytosolic markers were used and it was found that essentially no cytosolic contamination was present except in brain preparations. A bacterial protease was used along with digitonin fractionation to determine localization of the mitochondrial LDH. Approximately 80% of the LDH activity associated with heart and kidney mitochondrial preparations was on the inside compared to about 40% for liver. Lymphocyte mitochondrial LDH activity was about 70% on the inside. Cytosolic LDH-5 preferentially adheres to outer mitochondrial membrane of liver, kidney, and heart. Agarose gel electrophoresis showed LDH isozymes in mitochondria qualitatively similar to that of the corresponding cytosol except in kidney mitochondrial preparations, where a specific electrophoretic band was found which did not correspond to any of the common LDH isozymes.