Abstract
A possible role of membrane phospholipids in catalytic properties of carp brain mitochondrial monoamine oxidase (MAO) in both intact and delipidated membranes were studied before and after addition of some phospholipids. Deaminations of 5-HT and tyramine were greatly decreased by treatment with either phospholipase A2, C or D, but that of PEA was to a lesser extent. The sensitivity of MAO in the delipidated preparation to clorgyline and deprenyl was similar to that in the intact one; however, the amount of 3H-pargyline bound to MAO was found to be about half, and the Km values for the three substrates were extremely increased after delipidation. Among phospholipids tested, phosphatidylinositol(PI) most effectively and dose-dependently activated activity towards 5-HT in both intact and delipidated mitochondria, but the inhibitor sensitivity of MAO and the Km values for these substrates were not changed as compared before and after the PI addition. As a result, delipidation accounts for loss of activity through decreases in both the Km values and amount of active enzyme, but some phospholipids activate MAO activity without altering affinities towards substrates and selective MAO inhibitors.
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