[Analysis of ubiquitin-dependent regulation of the monoamine oxidase sensitivity to proteolysis and specific inhibition by pargyline].

Insertion of exogenous ubiquitin into rat brain mitochondria in the presence of ATP and the ATP-regenerating system (creatine phosphate/creatine phosphokinase) is accompanied by the increase in: i) sensitivity of mitochondrial monoamine oxidases A and B to proteolytic inactivation (by trypsin and papain, respectively); ii) inhibition by mechanism based inhibitor, pargyline; iii) in [3H]-pargyline insertion into mitochondria (+48 +/- 11%, p<0.01). There was almost fivefold increase in [3H]-pargyline incorporation into the fraction obtained by immunoprecipitation of mitochondrial proteins with anti-ubiquitin antiserum and protein A Sepharose. This suggests that MAO is a potential substrate for ubiquitination in vitro. However, the content of the tritium label in this fraction was less than 0.1% and not more than 0.25% of total radioactivity of [3H]pargyline bound to control and ATP-ubiquitin treated mitochondria, respectively. Insertion of ubiquitin into mitochondria did not influence molecular masses of [3H]-pargyline labeled proteins (MAO A and B). These results suggest that direct ubiquitination of MAO insignificantly contributes to marked changes in sensitivity of MAO A and MAO B to proteolysis and specific inhibition found under these experimental conditions. It is possible that more complex processes are involved into realization of these effects during ATP-dependent ubiquitin incorporation into mitochondria.