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KMID : 0376219660030010013
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Chonnam Medical Journal
1966 Volume.3 No. 1 p.13 ~ p.22
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Purification and Properties of Rabbit Heart Lactic Dehydrogenase With Special Reference to Substrate Inhibition
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Abstract
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1. Lactic dehydrogenase has been purified about 40 0-fold from rabbitt heart by first treating the heart extract with heat at 600C for 20 minutes followed -by fractionation with ammonium sulfate and hydroxylapatite.
2. The purified enzyme showed a single sharp band upon starch gel electrophoresis. The Michaelis constant (Km) value for pyruvate was 0.1 mM and , for DL-lactate 18 mM The: Km value -for lactate was not affected with pH change of the reaction. However, the maximal velocity with lactate was much lower at pH 7.4 than at pH 10.0.
3. The inhibition of the enzyme by high substrate concentration of pyruvate or lactate was much varied depending on the temperature of the reaction at 250C and at 37°C. Thus, at 25°C, the heart type enzyme, in contrast to the muscle type, showed a marked inhibition with high concentration of pyruvate and lactate. At 37°C, however, the heart type enzyme c ose y resembled the muscle type in extent of inhibition by substrate, both types showing a little inhibition by pyruvate with no inhibition by lactate.
4. From these results, it is discussed that the similarity of both type isozymes in degree of substrate inhibition at 37°C is incompatible with the theory based on the observation at 25°C that the heart type predominates in aerobic tissues while the muscle type predominates in anaerobic tissues.
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