[Isolation, purification and structure of molecules of a vasoactive component from rabbit skeletal muscle]. / Vydelenie, ochistka i struktura molekuly vazoaktivnogo komponenta iz skeletnykh myshts krolika.

A low molecular weight factor with pronounced vasoactive properties has been isolated from rabbit muscle. The procedure for lyophilized tissue extract purification included fractional methanol extraction with subsequent column chromatography on TSK-GEL Toyopearl, DEAE-Toyopearl 650 ion-exchanger and Sephadex G-10. The resulting preparation was homogeneous as evidenced from reversed phase HPLC. The structure of the factor was examined by using UV- and IR-spectrophotometry as well as by PMR and 13C-NMR. It was found that the vasoactive factor includes an inosine nucleotide structure covalently bound to a di- or tri-alanine peptide while the phosphate group is free. It is suggested that the binding of the peptide to the inosine moiety occurs via a C-terminal carboxyl of the peptide and pentose hydroxyls. It seems probable that the vasoactive effect is a result of esterification of the purine nucleotides with the peptide.

[Quinone-reducing activity of thrombocytes]. / Khinonredutsiruiushchaia aktivnost' trombotsitov.

NAD/P/H: quinone-oxidoreductase activity was determined in human thrombocytes using spectrophotometric and polarographic methods. Detergents, vitamins K3 and K1, ADP-induced aggregation of the thrombocytes were shown to affect the thrombocytic guinone-reductase activity. Possible localization of quinone-reductase in thrombocytes and its importance for the state of thrombocytic membrane are discussed.

[Mitochondrial menadione reductase: kinetics and mechanism of the action in situ]. / Mitokhondrial'naia menadionreduktaza kinetika i mekhanizm deistviia fermenta in situ

The formal mechanism of action of menadion reductase localized in the membrane of intact mitochondria in the rebox reaction of 4-N (p-sulfoanilin)-5-methoxy-1,2-benzoquinone with NADH as an electron donor has been studied by the stationary kinetics method. It has been shown that the mitochondrial menadion reductase incorporated into the membrane functions according to the "ping-pong" mechanism, similar to the functioning of the free enzyme. However, in this case an inhibitory effect of NADH has been noticed. A phenomenological equation, which is in a good accordance with the experimental data, has been suggested. Luminescence studies showed that a specific NADH-binding site located outside the active centre exists in the enzyme molecule. The model of the mechanism of the enzyme substrate inhibition in situ, responsible for a change in the conformation of the apoenzyme occurs upon NADH binding, is discussed.

[Properties and reaction mechanism of mitochondrial menadione reductase]. / Svoistva i kineticheskii mekhanizm deistviia mitokhondrial'noi menadionreduktazy

An isolation procedure of mitochondrial menadione reductase from rat liver using an ethanol-ether extraction for solubilization of the enzyme is described. The enzyme was purified 930-fold. The molecular weight of mitochondrial menadione reductase is 62,000. According to spectroscopic and enzymic analysis the prosthetic group of the enzyme was identified as FAD. Mitochondrial menadione reductase is inhibitied by dicumarol and p-chloromecuribenzoate. The enzyme is characterized by a group substrate specificity towards quinones. A high catalytic activity of menadione reductase towards 4-aniline-5-methoxy-1,2-benzoquinone (AMOBQ), and 4-N-(p-sulfoanilino)-5-methoxy-1,2-benzoquinone (AMOBQS) as acceptors was demonstrated. It was shown that the reduction of these orto-benzoquinones by NAD(P) H follows the "ping-pong" kinetics. The kinetic constants for NAD(P)H,AMOBQ and and AMOBQS were determined.