Electrochemical detection of biogenic amines following acylation by N-hydroxysuccinimide esters

Assay for acetyl-CoA:arylamine N-acetyltransferase by high-performance liquid chromatography applied to serotonin N-acetylation

A specific assay to measure the activity of the enzyme acetyl-CoA:arylamine N-acetyltransferase (EC 2.3.1.5) from pigeon liver is described. The assay is based on the HPLC analysis of N-acetylserotonin formed by the enzymatic reaction. A reversed-phase column (Spherisorb 5-microns ODS 2; 150 x 3.2 mm) eluted with 0.1 M sodium acetate (pH 4.75)/methanol (75:25) permits baseline separation of serotonin and N-acetylserotonin within 5.3 min. Several variables on the enzyme reaction were studied to obtain maximum activity. The enzyme is most active in glycine buffer at pH 9.5. The apparent Km value for serotonin (at 0.6 mM CoASAc) is 0.246 mM and 9.9 microM for CoASAc (at 1.5 mM serotonin). To avoid acetyl-CoA or N-acetylserotonin consumption in side-reactions, the enzyme was purified. A two-step purification process (ammonium sulfate fractionation and affinity chromatography on immobilised amethopterin) yielded 60-70% of the initial enzyme activity with a purification factor of 455-560.

Liquid chromatographic assay for cerebrospinal fluid normetanephrine

A method for quantitation of normetanephrine in human cerebrospinal fluid is described. An amine-specific reagent, sulfosuccinimidyl propionate, is used to obtain the lipid soluble N-propionyl derivative of normetanephrine, which can be separated and quantitated in presence of other biogenic amines by liquid chromatography with electrochemical detection. The method is reproducible, linear, and precise at the relatively low concentrations of unconjugated normetanephrine occurring in human cerebrospinal fluid. Hospitalized, drug-free, alcoholic patients were found to have cerebrospinal fluid unconjugated normetanephrine concentrations in the 0.5-1.5 nanomolar range. The practical limit of sensitivity for the method is about 0.025 pmole per ml of CSF.

Simultaneous determination of histamine and N tau-methylhistamine with high-performance liquid chromatography using electrochemical detection

We have developed a liquid chromatographic method which uses electrochemical detection for the simultaneous quantitation of histamine and N tau-methylhistamine in rat brain. The amines are derivatized with the water-soluble Bolton-Hunter reagent (sulfo B-H). Perchloric acid extracts of rat brains are chromatographed on a strong cation-exchange resin. The eluate is evaporated and allowed to react with sulfo B-H at pH 9.8 at room temperature. The derivatization is complete after 30 s vortexing. The derivatives are purified using a cellulose-phosphate fibrous cation exchanger. They are quantified with an electrochemical detector at a potential of 0.56 V after preoxidizing the sample at 0.47 V. The derivatives of histamine, N tau-methylhistamine, and N alpha-methylhistamine are completely separated without interfering peaks. Since no N alpha-methylhistamine was detected in rat brain it was used as an internal standard. The detection limits are 0.1 pmol of histamine and 0.2 pmol of N tau-methylhistamine. The precision of this method is high, with within-run and between-run coefficients of variation of 2-7% and linearity of 0.999. Both histamine and N tau-methylhistamine peak heights increased significantly and selectively after treatment with pargyline. Because of the high sensitivity, accuracy, and precision, the histamine and N tau-methylhistamine contents of single nuclei of the rat hypothalamus can be routinely quantified.