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Showing papers on "Catechol-O-methyl transferase published in 1976"


Journal ArticleDOI
TL;DR: A double-isotope, radioenzymatic assay for measuring dopamine, norepinephrine, and epinephrine in one sample is described, and several catechol compounds known to be O-methylated by COMT were examined for crossreactivity.
Abstract: A double-isotope, radioenzymatic assayfor measuring dopamine, norepinephrine, and epi-nephrine in one sample is described. The assayprocedure includes incubation, solvent extraction,and thin-layer chromatography. Dopamine, norepi-nephrine, and epinephrine were incubated withcatechol-O-methyl transferase (COMT) and [3H]S-adenosyl methionine ([3H]SAM) and were convertedto the O-methylated tritiated derivatives: [3H]meth-oxytyramine, [3H]normetanephrine, and [3H]meta-nephrine, respectively. After several extractionsteps, the O-methylated products were purified bymeans of two-dimensional, thin-layer chromatogra-phy using silica gel. The thin-layer chromatographicsystem resulted in complete separation of the threeO-methylated compounds with an overlap of only1-2%. The assay was linear from 0 to 5 ng for eachcatecholamine and had a sensitivity of 10-30 pg. Theaddition of large amounts of plasma reduced theactivity of COMT, but increasing the magnesiumconcentration in the incubation mixture and the addition of E...

199 citations


Journal ArticleDOI
TL;DR: The biochemical characteristics of soluble catechol‐O‐methyltransferase (COMT) activity in rat erythrocytes were compared with the properties of the soluble enzyme in rat liver, heart, and brain to measure COMT by a procedure that avoided artifacts of some other assay procedures including inhibition of the enzyme by endogenous calcium.
Abstract: The biochemical characteristics of soluble catechol-O-methyltransferase (COMT) activity in rat erythrocytes were compared with the properties of the soluble enzyme in rat liver, heart, and brain. COMT was measured by a procedure that avoided artifacts of some other assay procedures including inhibition of the enzyme by endogenous calcium. After the removal of calcium from the reaction mixture the apparent Michaelis-Menten constants for the two cosubstrates of the COMT reaction, S-adenosyl-1-methionine (SAM) and 3,4-dihydroxybenzoic acid (DBA), were similar in tissue preparations of rat liver, brain, heart and blood. The apparent Km values for the four tissues ranged from 5.7 to 6.7 x 10(-6) M and from 0.9-1.4 x 10(-4) M for SAM and DBA, respectively. The optimal pH and the optimal concentration of magnesium for the assay of red blood cell COMT were also similar to those for the enzyme in the three other rat tissues. After the removal of endogenous calcium, COMT activity in all four tissues was inhibited by the addition of calcium, and the [CaCl2] necessary to inhibit the enzyme activity 50% was 3-5 x 10(-4) M in all cases. The relative activities of COMT in the rat heart, brain, erythrocyte, and liver when expressed per g tissue or per ml of packed red blood cells were 1 to 1.15 to 1.58 to 140, respectively.

48 citations


Journal ArticleDOI
TL;DR: It is concluded that 6-aminodopamine-p-quinone (6-NH2DAQ) is perhaps the most toxic species toward catechol O-methyltransferase (COMT), however, the aminochromes which are formed from 6- NH2DAQ are also effective in inactivating COMT.
Abstract: 6-Aminodopamine (6-NH2DA) and various analogs of 6-NH2DA have been evaluated for their ability to inactivate purified catechol O-methyltransferase (COMT) in vitro. The inactivation of COMT by these agents could be prevented by including an antioxidant in the preincubation mixture or by excluding oxygen; however, catalase did not protect the enzyme from inactivation. Substrate protection studies and kinetic studies suggested that the loss of enzyme activity resulted from the alkylation of an amino acid residue at the active site of COMT by the quinoid types products which were generated upon air oxidation of 6-NH2DA. In addition, we have explored in more detail the reactivity toward COMT of specific intermediates in the oxidation pathways of 6-NH2DA by using various 6-NH2DA analogs. From the above studies we have concluded that 6-aminodopamine-p-quinone (6-NH2DAQ) is perhaps the most toxic species toward COMT. However, the aminochromes which are formed from 6-NH2DAQ are also effective in inactivating COMT. The results of these studies have provided a useful model system for observing the interaction of 6-NH2DA and its oxidation products with proteins; in addition, it has provided additional insight into the topography of the active site of COMT.

23 citations


Journal Article
TL;DR: The rate of migration during electrophoresis of both bands of RBC COMT was the same in manic depressive, schizophrenic, and normal individuals, and results did not reveal genetic variations in the COMT molecule among these three groups.

18 citations


Journal ArticleDOI
TL;DR: A series of methylated analogues of 6-hydroxydopamine (6-OHDA) has been synthesized and evaluated as irreversible inhibitors of catechol O-methyltransferase (COMT) to elucidate the mechanism involved in the inactivation of this enzyme by 6- OHDA.
Abstract: A series of methylated analogues of 6-hydroxydopamine (6-OHDA) has been synthesized and evaluated as irreversible inhibitors of catechol O-methyltransferase (COMT). These analogues have been prepared in an effort to elucidate the mechanism involved in the inactivation of this enzyme by 6-OHDA. The analogues prepared had methyl groups incorporated in the 2 and/or 5 positions of 6-OHDA so as to block nucleophilic attakc at these positions in the corresponding oxidation products [6-hydroxydopamine-p-quinone (6-OHDAQ), aminochromes I and II]. Such 2- and/or 5-methylated 6-OHDA analogues were found to be inhibitors of COMT with the inactivation apparently resulting from modification of an essential amino acid residue at the active site of the enzyme. The activity of these analogues as inhibitors of COMT argues against a mechanism involving a 1,4 Michael addition reaction by a protein nucleophile at the 2 or 5 positions on 6-OHDAQ or on the corresponding aminochromes. Instead, an alternative mechanism is proposed to explain these data, which involves attack of a protein nucleophile at the carbonyl group in the 6 position of 6-OHDAQ or at the imine functionality on aminochromes I and II. The results of the present experiments have provided insight into the mechanism involved in inactivation of COMT by 6-OHDA. In addition, this study has provided considerable insight into the chemical reactivity of the electrophilic species generated after oxidation of 6-OHDA.

17 citations


Journal ArticleDOI
TL;DR: The characteristics of the inhibition of rat liver catechol- O -methyltransferase by La 3+ , Nd 3+ and Eu 3+ are similar to those of the inhibited COMT by Ca 2+, however, lanthanum, neodymium and europium are two to three orders of magnitude more potent inhibitors of COMT than is calcium.

10 citations


Journal ArticleDOI
TL;DR: The activity of the enzyme catechol‐O‐methyltransferase (COMT) was determined in the erythrocytes of normal and autistic children and it was found that the activity was higher in children with autism than in normal children.
Abstract: 1. The activity of the enzyme catechol-O-methyltransferase (COMT) was determined in the erythrocytes of normal and autistic children. 2. There was no difference in enzyme activity between the two groups, although in both the normal and autistic females the erythrocyte COMT activity showed considerable within-group variation. 3. When the erythrocyte homogenates were divided into particulate and soluble fractions, some differences were observed. The COMT activity in the soluble fraction was less in erythrocytes from autistic males than in those from control males, whereas that in autistic females was higher than in those from control females.

8 citations


Journal ArticleDOI
TL;DR: A series of 5 and 7-substituted 8-hydroxyquinolines was evaluated as inhibitors of catechol O-methyltransferase (COMT, E.C. 2.1.6) as mentioned in this paper.
Abstract: A series of 5- and 7-substituted 8-hydroxyquinolines was evaluated as inhibitors of catechol O-methyltransferase (COMT, E.C. 2.1.1.6). The electronic character of the substituents in the 5 position appeared to have only a small effect if any on the inhibitory activity of these compounds. A significant factor which contributes to the inhibitory activity of these compounds appears to be the nature of the 7-substituent. The structure-activity relationship for this series of inhibitors is discussed relative to the nature of the enzymatic binding site.

8 citations


Journal Article
TL;DR: The results obtained on COMT activity in the individual platelet populations separated by a discontinuous sucrose density gradient are remarkable higher than in the old and light populations and may reflect platelet senescence.
Abstract: COMT activity is present in many animal tissues, but there is no evidence on the presence or the functional role of COMT activity in platelets. The present work reports the results obtained on COMT activity in the individual platelet populations separated by a discontinuous sucrose density gradient. In the young platelet populations the activity is remarkable higher than in the old and light populations. Low values of COMT activity in the old platelets may reflect platelet senescence.

7 citations


Journal Article
TL;DR: The data suggest that thyroid hormone may influence the ontogenic patterns of NE metabolism in the brain, as indicated by its rate of depletion following alpha-methyl-p-tyrosine administration.
Abstract: The effect of thyroid hormone on norepinephrine (NE) metabolism was investigated in various regions of the developing rat brain. Neonatal hypothyroidism, induced by daily propylthiouracil injection starting at birth, caused an increase in NE levels in the brain stem and hypothalamus. The turnover of brain NE, as indicated by its rate of depletion following alpha-methyl-p-tyrosine administration, was decreased in the hypothalamus of 30-day-old hypothyroid rats but was unchanged in the brain stem and basal ganglia. The activities of monoamine oxidase (MAO) and catechol-o-methyl transferase (COMT) were decreased in certain brain regions of hypothyroid rats. The data suggest that thyroid hormone may influence the ontogenic patterns of NE metabolism in the brain.

7 citations


Journal Article
TL;DR: Interindividual as well as intraindividual differences in the biochemical characteristics of the two enzymes were remarkably low, the coefficient of variation was in the range of 30%.
Abstract: Controversal findings are reported with respect to alternations in activity of monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT) in psychoses. Initially we determined the interindividual differences of some biochemical properties of the two enzymes in normal control subjects. Platelet rich plasma and lysate of red blood cells, respectively, were used for assay. Enzyme activity was referred to mg of protein or mg hemoglobin and number of platelets, respectively. Substrates used for COMT assay were: 3,4-dihydroxybenzaldehyde and 3,4-dihydroxybenzoic acid; for MAO determination: tyramine, tryptamine and phenylethylamine. Interindividual as well as intraindividual differences in the biochemical characteristics (apparent Km, Vmax, IC50, meta/para ratio of O-methylation in vitro) were remarkably low, the coefficient of variation was in the range of 30%.

Journal ArticleDOI
TL;DR: In this paper, 6-Aminodopamine and various analogs of 6-NH2DA have been evaluated for their ability to inactivate purified catechol O-methyltransferase (COMT) in vitro.
Abstract: 6-Aminodopamine (6-NH2DA) and various analogs of 6-NH2DA have been evaluated for their ability to inactivate purified catechol O-methyltransferase (COMT) in vitro. The inactivation of COMT by these agents could be prevented by including an antioxidant in the preincubation mixture or by excluding oxygen; however, catalase did not protect the enzyme from inactivation. Substrate protection studies and kinetic studies suggested that the loss of enzyme activity resulted from the alkylation of an amino acid residue at the active site of COMT by the quinoid types products which were generated upon air oxidation of 6-NH2DA. In addition, we have explored in more detail the reactivity toward COMT of specific intermediates in the oxidation pathways of 6-NH2DA by using various 6-NH2DA analogs. From the above studies we have concluded that 6-aminodopamine-p-quinone (6-NH2DAQ) is perhaps the most toxic species toward COMT. However, the aminochromes which are formed from 6-NH2DAQ are also effective in inactivating COMT. The results of these studies have provided a useful model system for observing the interaction of 6-NH2DA and its oxidation products with proteins; in addition, it has provided additional insight into the topography of the active site of COMT.