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INHIBITION OF RAT BRAIN PHENOL SULPHOTRANSFERASE IN VITRO BY NORADRENALINE and DOPAMINE METABOLITES 1
Author(s) -
Pennings E. J. M.,
Vrielink R.,
Wolters W. L.,
Kempen G. M. J.
Publication year - 1976
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1976.tb05155.x
Subject(s) - chemistry , mandelic acid , normetanephrine , enzyme , dopamine , in vitro , substrate (aquarium) , stereochemistry , non competitive inhibition , biochemistry , phenol , homovanillic acid , organic chemistry , urine , medicine , receptor , serotonin , oceanography , geology
— Kinetic parameters of the sulphotransferase reaction in rat brain were investigated in vitro at pH 7.4. Evidence is presented that the enzyme phenol sulphotransferase (EC 2.8.2.1) can be assayed with 4‐methylumbelliferone or 3‐methoxy‐4‐hydroxyphenylethyleneglycol as the substrate. Both assays give identical V max values, whereas K m values are 0.026 m m and 0.039 m m , respectively. Normetanephrine, metanephrine and the catecholamines adrenaline and dopamine, having a positive charge on the side chain at pH 7.4, do not inhibit 4‐methylumbelliferone and 3‐methoxy‐4‐hydroxyphenylethy‐leneglycol sulphotransferase at this pH. Their deaminated metabolites 3,4‐dihydroxyphenylethyleneglycol, 3,4‐dihydroxymandelic acid, 3,4‐dihydroxyphenylacetic acid, 3‐methoxy‐4‐hydroxyphenylethylene glycol, 3‐methoxy‐4‐hydroxyphenethanol and 3‐methoxy‐4‐hydroxyphenylacetic acid inhibit both the enzyme activities. The type of inhibition is noncompetitive with the exception of 3‐methoxy‐4‐hydroxy‐phenylethyleneglycol, which is a competitive inhibitor of 4‐methylumbelliferone sulphation. 3‐Methoxy‐4‐hydroxy‐mandelic acid does not inhibit the enzyme activities. It is concluded that the catecholamines themselves are not sulphated by rat brain in vitro at pH 7.4.