[Changes in external membrane lipids of the mouse liver mitochondria and kinetic parameters of membrane-bound monoaminoxidase in vivo and in vitro]. / Modifikatsiia lipidov naruzhnoi membrany mitokhondrii pecheni myshei i kineticheskikh parametrov membranosviazannoi monoaminoksidazy in vivo i in vitro.

Influence of lipids on monoamine oxidase (MAO) activity in external mitochondrial membranes of mice liver cells was studied. Content of acidic phospholipids (phosphatidyl serine + phosphatidyl inositol) correlated with Km value of tyramine deamination. The data obtained suggest that these phospholipids are important for the surface membrane charge which determines MAO affinity to the substrate. Relationship was also found between the viscosity of lipid components and Km, Vmax and the rate of inhibition by an excess of the substrate. Thus, the structural state of membrane lipid components affects the MAO affinity to the substrate, catalytic activity of the enzyme and its sensitivity to regulatory effectors. Among the kinetic patterns maximal rate, i.e. catalytic activity of the enzyme, was distinctly dependent on the viscosity of lipid bilayer.

[Hydrazine derivative modification of the activity of brain mitochondrial monoamine oxidases]. / Modifitsirovanie aktivnosti mitokhondrial'nykh monoaminoksidaz mozga nekotorymi proizvodnymi gidrazina.

Treatment of bovine brain stem mitochondria with hydrazine derivatives, which inhibited the monoamine oxidase activity (substrate: 5-hydroxytryptamine), was accompanied by appearance of the properties to deaminate histamine and cadaverine at a high rate. The same phenomenon was observed in vivo after treatment of mice with the hydrazine derivatives. The dramatic increase in histamine deaminating activity in brain was accompanied by a decrease in the tissue concentration of histamine. The hydrazine derivatives are considered as prooxidants stimulating via a free-radical mechanism lipid peroxidation in methyloleate solutions and in biomembranes (ref. 5) and causing qualitative alteration (transformation) in catalytic properties of monoamine oxidases of the tyre A, which acquire the histamine deaminating activity. A certain correlation was noted between the prooxidant effect of the hydrazine derivatives and the modification of catalytic properties of the membrane bound monoamine oxidases of brain mitochondria in vitro and in vivo.

[Effect of D,L-malic acid dibenzylhydrazide on changes in the antioxidizing activity of lipids and monoamine oxidase activity in mouse organs]. / Izmenenie antiokislitel'noi aktivnosti lipidov organov myshei i aktivnosti monoaminokisdazy pri deistvii dibenzilgidrazida D,L-iablochnoi kisloty.

Administration of dibenzylhydracide of D,L-malic acid (inhibitor of monoamine oxidase) into animals caused not only inhibition but also transformation of the mitochondrial monoamine oxidase activity, which acquired the property to deaminate histamine. Effect of the monoamine oxidase inhibitor on the antioxidative activity of lipids from mouse liver and brain tissues was studied. Effect of the dose administered and of the period of its action after administration were characterized. Influence of the inhibitor on oxidation of methyloleate was also studied in a model system. The data obtained suggest that the transformation-producing effect of the substance was not related to its immudiate action on the enzyme molecule but was apparently due to its influence on the intensity of lipid peroxidation in membranes.