Simple purification of aromatic L-amino acid decarboxylase from human pheochromocytoma using high-performance liquid chromatography

Reduction of aromatic L-amino acid decarboxylase activity in clonal pheochromocytoma PC12h cells by culture in the presence of N-methyl-4-phenylpyridinium ion (MPP+)

Rat clonal pheochromocytoma PC12h cells were cultured in the presence of N-methyl-4-phenylpyridinium ion (MPP+) and the activity of aromatic L-amino acid decarboxylase (AADC) was reduced after 3 and 6 days of culture. AADC activity in control cells was increased markedly by addition of pyridoxal 5-phosphate (PLP) to the reaction mixture, but that in the cells cultured in the presence of MPP+ was not increased by addition of PLP. After 6 days culture, AADC activity was almost negligible in the cells cultured in the presence of 1 mM MPP+, but PLP concentration in the cells was not reduced. AADC in the cells cultured in the presence of MPP+ reduced the affinity to PLP, but the affinity to a substrate, L-DOPA, did not change. Intracellular concentration of AADC protein was not reduced, as shown by an immunobinding assay with anti-AADC antibody. These data indicate that MPP+ may induce conformational changes in AADC protein and reduces its affinity to the cofactor, PLP.

Aromatic L-amino acid decarboxylase-immunoreactive neurons in and around the cerebrospinal fluid-contacting neurons of the central canal do not contain dopamine or serotonin in the mouse and rat spinal cord

Using a specific antibody against each of the 4 catecholamine-synthesizing enzymes, dopamine or serotonin, we compared the localization of these substances in rat and mouse spinal cord with two kinds of fixative, such as paraformaldehyde and glutaraldehyde, and two types of sectioning technique, i.e. cryostat and microslicer. In this study, we demonstrated aromatic L-amino acid decarboxylase (AADC)-like immunoreactivity (LI) in cerebrospinal fluid (CSF)-contacting neurons for the first time in the mouse. These cells and some AADC-immunoreactive cells localized outside the subependymal layer of mouse and rat spinal cord did not show tyrosine hydroxylase-, serotonin- and dopamine-LI with and without colchicine treatment.

Purification and characterization of aromatic L-amino acid decarboxylase from rat kidney and monoclonal antibody to the enzyme

Aromatic L-amino acid decarboxylase was purified from rat kidney to homogeneity, as judged by polyacrylamide gel electrophoresis, in the presence and absence of sodium dodecyl sulfate (SDS). The final preparation showed an activity of 3,4-dihydroxyphenylalanine (dopa) decarboxylation of approximately 11,000 nmol/min/mg of protein at 37 degrees C. The purified enzyme also catalyzed the decarboxylation of 5-hydroxytryptophan, tyrosine, tryptophan, and phenylalanine. The enzyme appeared to be composed of two identical subunits, each possessing a molecular weight of 48,000. The isoelectric point of the enzyme was estimated to be 6.7 in the presence of 8 M urea and 5.60-5.85 in its absence. To examine the identity of aromatic L-amino acid decarboxylase from various tissues, a monoclonal antibody directed against the enzyme from rat kidney was prepared. Immunotitration and analysis by antibody-affinity chromatography followed by SDS-polyacrylamide gel electrophoresis revealed that the enzymes from the striatum, adrenal medulla, pineal gland, liver, and kidney were indistinguishable with respect to immunological cross-reactivity and molecular size.

Purification of aromatic L-amino acid decarboxylase from bovine brain with a monoclonal antibody

Aromatic L-amino acid decarboxylase was purified from bovine brain for the first time by affinity chromatography using a monoclonal antibody to the enzyme, and it was compared with the decarboxylase purified from bovine adrenal medulla by the same procedure. The monoclonal antibody was produced from a hybridoma established for the enzyme highly purified from bovine adrenal medulla. The Mr values of brain and adrenal-medulla enzyme were both estimated to be approx. 100,000 by gel-permeation chromatography. SDS/polyacrylamide-gel electrophoresis revealed a single band with an apparent Mr of 50,000. Western immunoblot analysis showed that the antibody recognized each enzyme. With regard to substrate specificity, pH-dependence and effect of pyridoxal 5'-phosphate as a cofactor, both enzymes were similar.

Increase of catecholamines in mouse brain by systemic administration of gamma-glutamyl L-3,4-dihydroxyphenylalanine

We investigated the effect of systemic administration of gamma-glutamyl L-3,4-dihydroxyphenylalanine (gamma-Glu-DOPA) on catecholamine contents in the brain. gamma-Glu-DOPA was transformed to dopamine (DA) in vitro with brain homogenate by the sequential action of gamma-glutamyl transpeptidase and aromatic L-amino acid decarboxylase. Intraperitoneal injection of gamma-Glu-DOPA to mice increased DA markedly and noradrenaline (NA) moderately in the brain. The increase of endogenous DA was followed by elevation of the main DA metabolites (3,4-dihydroxyphenyl-acetic acid and homovanillic acid). These increases were in a dose-dependent manner. The maximal elevation of DA was observed within 30 min after administration of gamma-Glu-DOPA, but a substantial increase of NA was observed 2 h after the administration. These results suggest that gamma-Glu-DOPA may be applicable to the treatment of Parkinson's disease.

L-threo-3,4-dihydroxyphenylserine (DOPS) aldolase: a new enzyme cleaving DOPS into protocatechualdehyde and glycine

An enzyme which cleaves L-threo-3,4-dihydroxyphenylserine into protocatechualdehyde and glycine was demonstrated in extracts of human brains. Equimolar production of protocachualdehyde and glycine was quantitatively confirmed using high-performance liquid chromatography. In subcellular fractions of the brain, the highest enzyme activity was found in cytosol and soluble fraction. L-threo-DOPS proved to be the best substrate for this enzyme. The L-erythroisomer was less active and D-threo- and D-erythro-isomers were essentially inactive. The enzyme activity has an optimal pH around 7.4, and requires pyridoxal phosphate for maximal activity.

Uptake of L-threo-dihydroxyphenylserine into human brain synaptosomes

Out of four diastereoisomers of 3,4-dihydroxyphenylserine (DOPS), L-threo- and L-erythro-isomer were found to be taken up into human brain synaptosomes. The uptake of L-threo-DOPS was dependent on the temperature and sensitive to the metabolic inhibitors. The L-threo-DOPS uptake proved to be saturable and carrier-mediated transport with two different kinetic characteristics; a high-affinity and low-capacity and a low-affinity and high-capacity system. The apparent Km values of these two systems were obtained to be 28.6 microM and 2.47 mM, respectively. The high-affinity transport was inhibited by glycine, L-tyrosine, L-proline, L-serine, L-Dopa, L-tryptophan, and L-phenylalanine. The inhibition by L-tyrosine was competitive in regard to L-threo-DOPS. The L-threo-DOPS uptake was inhibited by 2,4-dinitrophenol, sodium cyanide and other uncouplers of oxidative phosphorylation and by ouabain, an inhibitor of Na+, K+-ATPase, indicating that the uptake is coupled to ATP hydrolysis. On the other hand, L-threo-DOPS uptake by the low-affinity system was not inhibited by metabolic inhibitors, indicating that it may be facilitated diffusion common to high concentrations of L-amino acids.

Inhibition of monoamine oxidase by 3,4-dihydroxyphenylserine

The effects of diastereomers of 3,4-dihydroxyphenylserine (DOPS) on the enzyme activity of monoamine oxidase (MAO) in human placenta and liver mitochondria were examined. Both L- and D-threo-DOPS were found to inhibit MAO-A in human placental mitochondria in competition with the substrate, and the Ki values for L- and D-threo-DOPS obtained were 68.3 and 125 microM, respectively. The inhibitory effect of L-threo-DOPS on both MAO-A and -B activity was confirmed in human liver mitochondria, and MAO-A was found to be more sensitive to the inhibitor. Other isomers of DOPS, L- and D-erythro-DOPS, were found to inhibit MAO activity, but the inhibition was noncompetitive with the substrate. The inhibitory effects of DOPS isomers were not affected by the presence of NSD-1055, an inhibitor of aromatic L-amino acid decarboxylase, suggesting that the inhibition is the direct effect of DOPS, and not of norepinephrine produced by the decarboxylase.

Occurrence of aromatic L-amino acid decarboxylase in human plasma and its assay by high-performance liquid chromatography with fluorescence detection

A high-performance liquid chromatographic method using fluorescence detection for assessing the activity of aromatic L-amino acid decarboxylase in human plasma is described. Dopamine, formed enzymatically from L-DOPA, and isoproterenol (internal standard) are chromatographed on a small ion-exchange cartridge (Toyopak SP) and derivatized with 1,2-diphenylethylenediamine. The derivatives are separated by reversed-phase chromatography on an Ultrasphere ODS column. The detection limit for dopamine formed enzymatically is 0.6 pmol per 500 microliter of enzyme reaction mixture. Aromatic L-amino acid decarboxylase in human plasma is very similar to that in rat kidney, with respect to optimum conditions for the enzyme reaction and gel chromatographic behaviour.