Showing papers on "Monoamine oxidase B published in 1971"

Monoamine oxidase in sympathetic nerves: a transmitter specific enzyme type.

Abstract: 1. When rat brain or superior cervical ganglion monoamine oxidase was incubated with increasing concentrations of clorgyline, using tyramine as substrate, the inhibition of the enzyme could be represented by a pair of sigmoidal curves joined by a horizontal region where inhibition was constant. Tyramine appeared to be metabolized by two enzymes, one of which was highly sensitive to clorgyline, designated A, whereas the other enzyme, designated B, was less sensitive to clorgyline. 2. The ratio of A/B activity for brain was 6/4 while in the ganglion it was 9/1. 3. When the experiments were repeated using noradrenaline as the substrate, the inhibition of the enzyme followed a simple sigmoidal curve where deamination was inhibited by low concentrations of clorgyline as observed with enzyme A. 4. We conclude that tyramine is deaminated by both A and B enzymes whereas noradrenaline is deaminated only by enzyme A, the enzyme which is most active in the ganglion. Our observations are consistent with the hypothesis that a specific intraneuronal monoamine oxidase plays an important role in the catabolism of noradrenaline in sympathetic nerves.

Occurrence and properties of monoamine oxidase in adrenergic neurons.

Abstract: —Monoamine oxidase activity of peripheral organs of various species has been examined after surgical, chemical and immunological sympathectomy to assess the proportion of enzyme activity in adrenergic neurons and in extraneuronal cells. Significant falls in monoamine oxidase activity of vas deferens, submaxillary gland, iris and spleen were seen after sympathetic denervation although not in heart, small intestine and kidney. It was suggested that a correlation exists between the extent of the fall in monoamine oxidase activity after sympathectomy and the density of sympathetic innervation of the control organ. Studies of monoamine oxidase activity in vas deferens after inhibition with clorgyline suggested multiple forms of monoamine oxidase. Differences in inhibitor sensitivity, substrate specificity and thermal inactivation of monoamine oxidase in normal and denervated vas deferens were found and it was suggested that differences exist in the properties of the neuronal and extraneuronal monoamine oxidase.

Possible new metabolites mediating actions of L-dopa.

Abstract: IT is generally assumed that the pharmacological actions of L-dopa (L-3,4-dihydroxyphenylalanine) are mediated through its conversion to dopamine. Thus, the specific value of L-dopa in the treatment of Parkinson's disease1–4 would lie in its ability to traverse the blood–brain barrier and undergo de-carboxylation in the parenchymal cells of the brain. It is likely that this mechanism operates physiologically in certain systems. But is dopamine the only metabolite mediating the action of L-dopa4–7? Some other simple derivative, formed in the brain by “conventional” pathways, may be pharmacologically active and responsible for the stimulation of dopamine-sensitive receptors that have been deprived of their normal presynaptic connexions through degenerative processes, as in Parkinson's disease, or by stereotaxically placed lesions in experimental animals8–10. Another possibility lies in the conversion of L-dopa or one of its immediate products to some quite different compound, for example by condensation of dopamine with an aldehyde to form a tetrahydroisoquinoline. Reactions of this type are known for pyridoxal and its phosphate11–13, as well as for 3,4-dihydroxyphenylacetaldehyde. The last compound arises from dopamine through the action of monoamine oxidase, and can condense non-enzymatically with dopamine to form tetrahydropapaveroline (nor-laudano-soline)14 as shown in Fig. 1. A Scruff's base is an intermediary in the reaction. Tetrahydropapaveroline possesses hypotensive activity14. It is conceivable that a benzyltetrahydroisoquinoline, derived from L-dopa in vivo, has at least some of the pharmacological activities ascribed to this amino-acid in Parkinson's disease7. The type reaction described here has been demonstrated in vivo;, in this case, 1-methyl-l,2,3,4-tetrahydroisoquinolines are formed15,16 by the condensation of catecholamines with acetaldehyde, the immediate dehydrogenation product of ethanol.

Multiple forms of monoamine oxidase in developing brain: tissue and substrate specificities

Abstract: Brains, hearts and livers from newborn and adult rats were assayed for monoamine oxidase activity using gel electrophoretic techniques. The results suggest that each of the tissues possesses multiple forms (isoenzymes) of monoamine oxidase and that these forms are different for the various tissues. Further, the forms of monoamine oxidase in the neonatal tissues differ from those in the corresponding adult tissue. These different forms of monoamine oxidase have different substrate specificities. Using 5-hydroxy[14C]tryptamine as substrate, we have demonstrated that the monoamine oxidase patterns appearing on the gel do indeed possess monoamine oxidase activity.

Alterations in Tyrosine Hydroxylase and Monoamine Oxidase Activity in Blood Vessels

Abstract: THE enzyme tyrosine hydroxylase1 (TH), which has been reported as the rate limiting step in noradrenaline biosynthesis, can be modified by nerve stimulation, cold2,3, exercise4, reser-pine, phenoxybenzamine, and monoamine oxidase inhibitors5–7. These treatments affect not only the enzyme in vitro but also catecholamine synthesis in vivo. Much of this information has come from studies with heart, brain, adrenals and spleen, but we found that blood vessels contain appreciable concentrations of noradrenaline8 and synthesize it in vivo from its precursor tyrosine. We now report that blood vessels have higher tyrosine hydroxylase activity than the heart and that this activity can be modified by reserpine and L-dihydroxyphenylalanine (L-dopa). Furthermore, the activity of tyrosine hydroxylase in the blood vessels of a spontaneously hypertensive rat differs from that in its normotensive control. We also found that the activity of the enzyme monoamine oxidase in the vasculature was affected by drugs and changes in blood pressure.

Effect of 6-hydroxydopamine on oxidative phosphorylation and on monoamine oxidase activity.

Abstract: In rat liver homogenates, 6-hydroxydopamine was as potent as 2,4-dinitrophenol in uncoupling oxidative phosphorylation. In a concentration which caused complete uncoupling of oxidative phosphorylation, 6-hydroxydopamine failed to affect the monoamine oxidase activity of rat liver homogenates; the enzyme activity was determined with tyramine as substrate. The results indicate that 6-hydroxydopamine has an effect on oxidative phosphorylation which is not entirely nonspecific. It is possible that this effect is involved in the degeneration of adrenergio nerve endings seen after 6-hydroxydopamine.

Inhibition Patterns of Monoamine Oxidase Isoenzymes: Clinical Implications

Abstract: Monoamine oxidase (EC 1.4.3.4; MAO) is an insoluble enzyme which is widespread in the body (for review, see Blaschko, 1952). Particularly high concentrations are present in the brain, liver and salivary glands. Within the cell, the enzyme is located predominantly in mitochondria, probably in the outer membrane (Schnaitman et al., 1967), although activity has been detected in the microsomal fraction of certain organs (de Champlain et al., 1969). MAO catalyses the oxidative deamination to an aldehyde of a number of physiologically occurring monoamines, including the catecholamines and 5-hydroxytryptamine.

Inhibition of monoamine oxidase by 3-amino-2-oxazolidinone and 2-hydroxy-ethylhydrazine.

Abstract: Die MAO-hemmende Aktivitat von 3-Amino-2-Oxazolidinon und von 2-Hydroxy-Athylhydrazin wird beschrieben.

Tricyclic dyes as monoamine oxidase inhibitors

Abstract: Highly pur i f ied spec imens of monoamine oxidase were obtained f r o m bovine l i ve r mi tochondr ia . Pyronine G and acr id ine orange NO in low concent ra t ions were shown to se lec t ive ly inhibit oxidative deaminat ion of t y r amine o r sero tonin by the p r e p a r a t i o n s of pur i f ied monoamine oxidase. These t r i cyc l i c dyes, in expe r imen t s in v i t ro , inhibit monoamine oxidase act ivi ty of r a t o r human l ive r mi tochondr ia to a much g r e a t e r deg ree than that of bovine l i ve r mitochondria . The abili ty of pyronine G and acr idine orange NO to inhibit monoamine oxidase act ivi ty under the expe r imen ta l conditions in vivo was conf i rmed by a r a d i o m e t r i c method.