ASSOCIATION OF MONO-AMINE OXIDASE WITH LIPID - COMPARATIVE-STUDY OF MITOCHONDRIA FROM NOVIKOFF HEPATOMA AND RAT-LIVER

Monoamine oxidase (MAO) from Novikoff hepatoma and liver of the rat host has been studied. MAO in the mitochondria from the fast growing hepatoma was determined to be predominantly of the A type by studies carried out with the irreversible inhibitors clorgyline and deprenyl. The enzyme from the host liver was similar to that reported for normal rat liver MAO. In order to investigate the role lipid may play in the genesis of different types of MAO, the hepatoma mitochondria were investigated as a model for type A MAO and compared to the host liver mitochondria which were shown to have both types of MAO activity. Phospholipid analysis of both hepatoma and host liver mitochondria revealed no significant difference in the proportion of outer membrane phospholipids. Delipidation with methyl ethyl ketone of both mitochondrial preparations resulted in the inactivation of type A MAO, which could be reactivated partially by mitochondrial lipids, but not by purified phosphatidylcholine. Low recovery of type B MAO after delipidation of the hepatoma mitochondria suggests that transformation of type A to type B MAO does not occur. Arrhenius plots of MAO activity revealed that type B MAO was sensitive to a phase transition of the outer mitochondrial membrane. The energy of activation of type B MAO as estimated by benzylamine deamination was reduced by 47 per cent at temperatures below 13°. Delipidation of mitochondria also resulted in a similar decrease in the energy of activation of type B MAO at all temperatures tested. Both types of MAO were shown to be labile to freeze/thawing as a result of delipidation. The results suggest that both types of MAO are integrally associated with the lipid environment of the outer mitochondrial membrane and that the association of lipid with the two types of MAO is different. © 1979.