Does isatin interact with rat brain monoamine oxidases in vivo?

Isatin is a reversible endogenous monoamine oxidase (MAO) inhibitor found in the brain. The influence of isatin on the degree of irreversible MAO inhibition by phenelzine and pargyline has been studied in vitro and in vivo experiments. In vitro 10 and 100 microM isatin reduced irreversible inhibition of MAO A and MAO B assayed after mitochondria wash. Pretreatment of rats with 'anxiogenic dose' of isatin (10 mg/kg) protected neither MAO A nor MAO B against subsequently administered phenelzine (10 mg/kg). 'Anticonvulsant' dose of isatin (80 mg/kg) reduced phenelzine-dependent inhibition of MAO B but not MAO A. Data obtained suggest that the anticonvulsant effect of isatin does not result from the inhibition of MAO A and the increase of monoamine level in the brain reported in few laboratories is apparently stipulated by a mechanism that does not involve MAO A inhibition.

The influence of some compounds commonly used in biochemical studies of mitochondria on the activity of monoamine oxidases.

It was previously described that low concentrations of sodium azide monoamine oxidase (MAO) B assayed by spectrophotometric measurement of benzaldehyde or by hydrogen peroxide accumulation. We failed to confirm this effect using radiometric determination of MAO activity. Tris or dinitrophenol inhibit MAO. The data suggest that some "regulatory effects" depend on the assay of MAO activity.

Chemical modification of the essential arginine residues of pyruvate dehydrogenase prevents its phosphorylation by kinase.

The mechanism of regulatory phosphorylation of the pyruvate dehydrogenase component (E1) of muscle pyruvate dehydrogenase complex was studied. Chemical modification of the arginine residues essential for substrate binding was shown to prevent incorporation of 32P from [gamma-32P]ATP into E1 catalyzed by kinase and to exclude completely the interaction of holo-E1 with pyruvate. It is proposed that negatively charged phosphoseryl residues may compete with pyruvate for the active site arginine and thereby block the substrate binding.

[Association of rabbit skeletal muscle phosphorylase kinase with sarcoplasmic reticulum membranes]. / Assotsiatsiia kinazy fosforilazy skeletnykh myshts krolika s membranami sarkoplazmaticheskogo retikuluma.

The binding of phosphorylase kinase to sarcoplasmic reticulum has been studied using gel chromatography. The presence of Ca2+, Mg2+ and glycogen was found to be necessary for the maximal binding. The phosphorylase kinase adsorbed on sarcoplasmic reticulum is capable of phosphorylating exogenous phosphorylase b. Phosphorylase kinase was shown to take no part in the phosphorylation of sarcoplasmic reticulum proteins. Exogenous calmodulin initiates the incorporation of [gamma-32P] of ATP into sarcoplasmic reticulum proteins. The data obtained point to a possibility that another Ca(2+)-calmodulin-dependent protein kinase may participate in the phosphorylation of sarcoplasmic proteins.

[Interaction of phosphorylase kinase with thin filament proteins of rabbit skeletal muscles]. / Vzaimodeistvie kinazy fosforilazy s belkami tonkikh filamentov skeletnykh myshts krolika.

The binding of phosphorylase kinase to thin filaments and their effects on the enzyme activity as well as the contribution of the enzyme to contractile protein phosphorylation have been studied. The data obtained suggest that the kinase binding to thin filaments is controlled by the regulatory proteins, troponin and tropomyosin. The bulk of the enzyme is bound to the F-actin-tropomyosin-troponin complex which activates the enzyme in a far greater degree than each of its constituent components. Ca2+ and ATP control the kinase binding to F-actin. ATP increases the enzyme binding 6-fold; Ca2+ decrease the S0.5 value for F-actin 5-fold. In acetone powder extracts phosphorylase kinase phosphorylates thin filament-bound phosphorylase b, troponin T and troponin I as well as 51-58 kDa and 114 kDa proteins. These results suggest that phosphorylase kinase plays a role in the mechanism of synchronization of glycogenolysis and muscle contraction rates.

[The role of phosphorylase kinase subunits in interaction with glycogen]. / Rol' sub''edinits kinazy fosforilazy vo vzaimodeistii s glikogenom.

The interaction of rabbit skeletal muscle phosphorylase kinase with CNBr-activated glycogen results in the formation of a covalent complex. The non-bound kinase was removed by chromatography on DEAE-cellulose and phenyl-Sepharose. The amount of the bound protein increased with an increase in the number of activated groups in the glycogen molecule; the enzyme activity was thereby decreased. The kinase covalently and non-covalently bound to glycogen exhibited a higher affinity for the protein substrate (phosphorylase b) as well as for Mg2+ and Ca2+ than did the kinase in the absence of glycogen. Electrophoresis performed under denaturating conditions showed that the gamma-subunit of phosphorylase kinase is responsible for the enzyme binding to CNBr-glycogen. The effect of cross-linking reagents (glutaric aldehyde, 1.5-difluoro-2.4-dinitrobenzene) on the binding of phosphorylase kinase subunits was studied. Glycogen afforded protection of the gamma-subunit from the cross-linking to other enzyme subunits. An analysis of the subunit composition of phosphorylase kinase covalently bound to CNBr-glycogen and of the enzyme treated with cross-linking reagents in the presence of glycogen-revealed that the gamma-subunit is involved in the specific binding of phosphorylase kinase to glycogen.

[Regulation of the activity of rabbit skeletal muscle phosphorylase kinase by glycogen]. / Reguliatsiia aktivnosti kinazy fosforilazy iz skeletnykh myshts krolika glikogenom.

The effects of glycogen on the non-activated and activated forms of phosphorylase kinase were studied. It was found that in the presence of glycogen the activity of non-activated kinase at pH 6.8 and 8.2 and that of the activated (in the course of phosphorylation) form are enhanced. The degree of activation depends on glycogen concentration. At saturating concentrations, this enzyme activity increases 2-3-fold; the enzyme affinity for the protein substrate, phosphorylase b, also shows an increase. The polysaccharide has no effect on the activity of phosphorylase kinase stimulated by limited proteolysis. In the presence of glycogen, the rate of autocatalytic phosphorylation of the enzyme is increased. Glycogen stabilizes the enzyme activity upon dilution. The experimental results suggest that the polysaccharide directly affects the phosphorylase kinase molecule. The maximal binding was shown to occur at the enzyme/polysaccharide ratio of 1:10 (w/w) in the presence of Ca2+ and Mg2+.