FAD-dependent malate dehydrogenase from Mycobacterium smegmatis: activation of the lipid-depleted enzyme by incorporation into cardiolipin liposome.

The lipid-depleted, enzymatically inactive malate dehydrogenase isolated from Mycobacterium smegmatis membrane was found to be incorporated spontaneously into cardiolipin liposome, but not into phosphatidylcholine liposome, as was revealed by electron spin resonance spectra with the use of 5-doxylstearic acid as a spin probe in the phospholipid liposomes. In addition, sucrose density gradient centrifugation in 0.5 M KCl showed hydrophobic interaction of the enzyme with cardiolipin liposome and further proved that the enzyme thus interacted hydrophobically with cardiolipin liposome became enzymatically active. From the results obtained above, it was concluded that the lipid-depleted, enzymatically inactive malate dehydrogenase isolated from M. smegmatis membrane was found to be activated by incorporating into the hydrophobic region of cardiolipin liposome.