Showing papers on "Catechol-O-methyl transferase published in 1979"

Catechol-O-methyltransferase: thermolabile enzyme in erythrocytes of subjects homozygous for allele for low activity

Abstract: Low catechol-O-methyltransferase (COMT) activity (less than 8 units per milliliter) in the human erythrocyte is inherited as an autosomal recessive trait (COMTL). The average half-life of COMT in erythrocyte lysates incubated at 48 degrees C was significantly shorter in lysates from three subjects with low enzyme activity than in lysates from three subjects with high enzyme activity (12.5 +/- 0.9 minutes compared with 21.2 +/- 1.4 minutes, P less than .01). When the ratios of COMT activities in lysates heated at 48 degrees C for 15 minutes to enzyme activities in unheated samples were used as a measure of enzyme thermostability in blood samples from 316 randomly selected subjects, the ratios were significantly less for subjects with low enzyme activity than for subjects with higher enzyme activity. The presense of thermolabile COMT in blood of individuals homozygous for COMTL raises the possibility that the locus COMT may represent the structural gene for the human enzyme.

Monoamine oxidase and catechol-O-methyltransferase activity in hamster and rat insulinomas.

Abstract: Hamster and rat insulinomas were assayed for norepinephrine, dopamine and serotonin concentration and for monoamine oxidase and catechol-o-ethyltransferase (COMT) activity. The concentration of norepinephrine (mean 0.55 μmol/kg, range <0.20 to 2.64 μmol/kg) and serotonin (mean 5.22 μmol/kg, range <0.6 to 26.5 μmol/kg) in hamster insulinomas were comparable to previously reported concentrations. Dopamine concentration (mean 0.34 μmol/kg, range <0.20 to 0.95 μmol/kg) was only 2 to 2.5% of that reported previously. Monoamine oxidase activity of the hamster and rat insulinomas were comparable to those of normal hamster islets. In contrast, the COMT activity of both insulinomas was much greater than the COMT activity of normal pancreatic islets of both species and was greater than in several other tissues and tumours. The tumour COMT, which was predominantly in the cytosol, was Mg2+ dependent and had a comparable sensitivity to inhibition by tropolone as purified beef-liver COMT. Hamster insulinoma monoamine oxidase was more sensitive than rat insulinoma monoamine oxidase to inhibition by tranylcypromine and deprenyl, while rat insulinoma monoamine oxidase was more sensitive to inhibition by clorgyline and was more heat labile.

Immunocytochemical localization of catechol-o-methyltransferase in cardiovascular tissues

Abstract: Immunocytochemical localization of catechol-O-methyltransferase (COMT) in cardiovascular tissues of the rat demonstrated the presence of COMT in aortic and capillary endothelial cells and in myocardial cells. Smooth muscle cells of the aorta and coronary vasculature did not stain positively for COMT. Ultrastructurally, the enzyme was found to be cytoplasmic and also associated with plasma membranes and basement membranes (external laminae - myocardial cells; basal laminae - endothelial cells) in both positive cell types.

Developmental changes in the activity of catechol-O-methyl transferase in rat and rabbit fetuses.

Abstract: Variations in the activity of catechol-O-methyltransferase (COMT) in peripheral organs in the brain of rat and rabbit fetus during development have been studied. The pattern of changes in COMT activity in rat fetus differed to a great extent according to the respective organs studied. In kidney and liver sharp declines occurred between days 18 and 20 and days 16 and 18 of fetal life respectively, followed by progressive increases up to onset of birth. Brain COMT of rat fetus declined progressively from day 16 of fetal life up to 0 hours after birth, while COMPT activity in adrenal and heart showed its maximum value at the 20th day of fetal life and at 0 hours after birth respectively. In the contrary, the developmental changes in activity of rabbit fetus were very similar in all the organs except in the adrenals, since it decreased between day 24 to 8 hours after birth in heart, liver, brain and kidney. In the adrenals an important increase could be seen between the 24th and 28th days of fetal life. Rat COMT activity during 4 and 8 hours of postnatal life in heart, liver and kidney declined from 0-hour value but it increased in the brain and adrenals. COMT in rabbit increased after birth in all the organs studied. The results suggest that metabolic degradation of catecholamines by 3-O-methylation in rat and rabbit fetus may have different developmental patterns to some extent according to the physiological status of the organ concerned. These species related differences for monoamine inactivation during fetal development may suggest a physiological role for COMT as a marker of the maturation of the autonomic nervous system.

The time course of brain and blood catecholamines, catechol O-methyltransferase, and amino acids in rats convulsed by oxygen at high pressure

Abstract: The time course of changes in blood and brain catecholamines, catechol O-methyltransferase (COMT), ammonia, and amino acids leading to convulsion by high pressure oxygen breathing (OHP) in rats has been investigated. Brain catecholamines were suppressed by OHP. They changed in phase with brain COMT concentration and consequently were not due to the action of this degrading enzyme. Convulsive actions seem not to be influenced by brain catecholamine concentration. Blood adrenaline concentrations are, however, significantly elevated both prior to and during convulsions. In both brain and blood, ammonia concentration increases, glutamate decreases, and glutamine-aspargine increases. It is proposed that the efficacy of the glutamate-glutamine ammonia buffering system in blood and brain is important in the prevention of the onset of convulsions but that when brain gamma-aminobutyric acid is depressed to critical levels, convulsions result.

Catechol-o-methyltransferase biochemical genetics

Abstract: Low human erythrocyte (RBC) catechol-O-methyltransferase (COMT) activity (< 8 units/ml) is inherited as an autosomal recessive trait. Approximately 25% of a randomly selected population is homozygous for the allele for low RBC COMT. The enzyme in the erythrocytes of these subjects is biochemically different from that in subjects with higher enzyme activity, an observation that raises the possibility that this locus represents the structural gene for COMT in man.