Mitochondrial monoamine oxidase of rat liver: Reversible qualitative alterations in catalytic properties

Abstract

1. 1.|Preincubation of rat liver mitochondrial membranes under aerobic conditions in the presence of Cu 2+ (but not of other metal ions) caused a significant decrease in monoamine oxidase (monoamine: oxygen oxidoreductase, EC 1.4.3.4) activity and induced the ability to deaminate substrates of diamine oxidase (diamine: oxygen oxidoreductase (deaminating), EC 1.4.3.6) (histamine and some diamines) and AMP. At the same time, the content of SH groups in the mitochondrial membranes decreased. 2. 2.|Preincubation of highly purified rat liver mitochondrial monoamine oxidase in the presence of Cu 2+ under aerobic conditions decreased the rate of deamination of monoamines and induced the ability to deaminate histamine, some diamines and AMP. These alterations (transformation) in enzymatic properties of monoamine oxidase were accompanied by a decrease in content of SH groups (from 8 to 1 per 10 5 g of protein) in the enzyme. The decrease in content of SH groups was probably due to their partial oxidation. The modified enzyme was insensitive to specific monoamine oxidase inhibitors (pargyline, tranylcypromine), but it was inhibited by some carbonyl reagents (hydroxylamine, isoniazid). 3. 3.|Qualitative alterations in catalytic properties of monoamine oxidase and the accompanying decrease in content of SH groups were observed after treatment of the enzyme with oxidized oleic acid. 4. 4.|Pretreatment of highly purified rat liver monoamine oxidase with specific irreversible monoamine oxidase inhibitors prevented appearance of the histamine deaminating activity in the course of subsequent incubation in the presence of Cu 2+. 5. 5.|Pretreatment of highly purified monoamine oxidase with alkylating agents ( N-ethylmaleimide, iodoacetamide) did not alter the catalytic properties of monoamine oxidase qualitatively, but prevented the development of these alterations in the course of subsequent incubation of the enzyme in the presence of Cu 2+. 6. 6.|Qualitative alteration in catalytic properties of monoamine oxidase (preincubated in presence of Cu 2+ or treated with oxidized oleic acid) was partially reversed by treatment of the enzyme with reducing agents (NaBH 4, reduced glutathione, Na 3AsO 3).