Comparative studies of purified and reconstituted monoamine oxidase from bovine liver mitochondria.

Monoamine oxidase, a strictly membrane-bound flavoenzyme, has been purified using a modified procedure recently developed. Probably similarly to other preparations known from the literature, the enzyme solubilizes to a clear suspension, which represents large clusters ranging in size from 5 to 50 nm containing appreciable amounts of residual lipids. The purified and reconstituted enzymes are inhibited differently by deoxycholate. In contrast to deoxycholate, Triton X-100 does not inhibit the purified enzyme, but rather disintegrates the lipid-enzyme clusters to the smallest active units. However, removal of the detergent leads to reconglomeration to larger lipid-enzyme aggregates. Using the irreversible destruction of the enzyme by deoxycholate as assay, reconstitution of the enzyme with exogeneous lipids has been studied. All basic enzyme properties, such as stability, maximal activity (V), Michaelis constant (Km), pH- and temperature-dependence of the purified and reconstituted systems, are significantly different.