Deviation supersensitivity and inhibition of saturable sites of loss

Separation methods for catechol O-methyltransferase activity assay: physiological and pathophysiological relevance

Catechol O-methyltransferase (COMT) transfers a methyl group from S-adenosyl-L-methionine to the catechol substrate in the presence of magnesium. After the characterisation of COMT more than four decades ago, a wide variety of COMT enzyme assays have been introduced. COMT activity analysis usually consists of the handling of the sample and incubation followed by separation and detection of the reaction products. Several of these assays are validated, reliable and sensitive. Besides the studies of the basic properties of COMT, the activity assay has also been applied to explore the relation of COMT to various disease states or disorders. In addition, COMT activity analysis has been applied clinically since COMT inhibitors have been introduced as adjuvant drugs in the treatment of Parkinson's disease.

Supersensitivity to catecholamines after inhibition of extraneuronal uptake (uptake2) or O-methylation

The influence of inhibition of uptake2 and of O-methylation on beta-adrenoceptor-mediated responses of guinea-pig trachea and rat uterus to some catecholamines was compared. The responses were more markedly enhanced by inhibition of O-methylation (by U-0521) than by inhibition of uptake2 (by hydrocortisone). The ranking order for the degree of super-sensitivity caused by either U-0521 or hydrocortisone was different in the two tissues, suggesting differences between the O-methylating systems of those tissues. In experiments with 3H-isoprenaline metabolism, hydrocortisone had a weak inhibitory effect on O-methylation in both tissues.

A simplified procedure for the fractionation of Tityus serrulatus venom: isolation and partial characterization of TsTX-IV, a new neurotoxin

Five toxins from the venom of the Brazilian scorpion Tityus serrulatus were purified to homogeneity by a combination of ion exchange chromatography with ammonium bicarbonate buffer (pH 7.8) on CM-cellulose-52 and rechromatography on the same resin equilibrated with ammonium acetate buffer (pH 4.7). Four of these proteins, obtained in one or two steps in high yield and lethality (named toxins IX3, IX5, and X4 and XIII) were shown to be identical with other toxins already described. A fifth one, TsTX-IV, is reported as a new toxin. Except for IX3, which showed Gly as the sole N-terminal residue, the other four toxins showed Lys. TsTX-IV has an approximate mol. wt of 6880, an i.v. LD50, in mice, of 826 +/- 156 micrograms/kg and an intracisternal LD50 of 11 +/- 9 micrograms/kg, compared to 375 +/- 45 and 4.9 +/- 0.8, respectively, for the whole venom extract. It has 61 amino acid residues and an amino acid composition different from that of any other toxin from Tityus serrulatus venom so far described. Toxins IX5, TsTX-IV and XIII induced a prejunctional type of supersensitivity on the guinea pig vas deferens, probably due to an increased release of noradrenaline.

The guinea-pig trachea O-methylating system is more effective in modulating beta 2- than beta 1-adrenoceptor-mediated responses to isoprenaline

Assuming that responses of the guinea-pig trachea to isoprenaline in the presence of atenolol (10 mumol L-1) are exclusively, or at least predominantly, beta 2-adrenoceptor mediated and that responses to isoprenaline in the presence of ICI 118,551 (erythro-DL-1(7-methylindan-4-yloxyl)-3-isopropylaminobut an-2-ol) (1 nmol L-1) are exclusively, or at least predominantly beta 1-adrenoceptor mediated, the influence of inhibition of COMT by U-0521 (dehydroxy-2-methyl propiophenone) (50 mumol L-1) has been compared in both conditions. U-0521 enhanced beta 2-adrenoceptor mediated responses to isoprenaline 3.3-fold, while those mediated by beta 1-adrenoceptors were enhanced only 2.2-fold. It is concluded that in guinea-pig trachea COMT activity is functionally more effective in modulating responses which are mediated by beta 2-adrenoceptors than responses mediated by beta 1-adrenoceptors.