Intracellular localization of phenol sulphotransferase in rat brain

Sulfate esters of hydroxy amino acids as stereospecific glutamate receptor agonists

Enantiomerically pure sulfate esters of the hydroxy amino acids homoserine, hydroxyproline and 4-hydroxypipecolic acid were synthesized and tested on alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors present in the mice cortical wedge preparation and on NMDA receptors present in the myenteric plexus of the guinea pig with the aim of finding new possible endogenous ligands (either agonists or antagonists) for excitatory amino acid receptors. The linear and flexible compound S-homoserine sulfate caused a depolarization of both AMPA and NMDA receptors. In the cortex its agonist action had an EC50 of 150 microM for NMDA and 300 microM for AMPA receptors and in the myenteric plexus its EC50 was 600 microM. The stereoisomer R-homoserine sulfate did not depolarize the cortical wedges and failed to cause ileal contraction up to a concentration of 500 microM. Among the four possible stereoisomers of 4-hydroxyproline sulfate, which are rigid structures and may be regarded as cyclization forms of homoserine sulfate, t-S-hydroxyproline sulfate was a selective AMPA receptor agonist with an EC50 of 70 microM in the cortex. The other three isomers were not active as agonists up to 500 microM and none of them had antagonist activity. Finally, t-4-hydroxy-S-pipecolic acid-4-sulfate, a superior homologue of t-S-hydroxyproline sulfate, was found to be one of the most potent and selective NMDA receptor agonists so far described with an EC50 of 0.7 microM in the cortex and 250 microM in the myenteric plexus.(ABSTRACT TRUNCATED AT 250 WORDS)

Formation and utilization of the active sulfate donor [35S]3'-phosphoadenosine 5'-phosphosulfate in brain slices: effects of depolarizing agents

The accumulation and utilization of [35S]3'-phosphoadenosine 5'-phosphosulfate (PAPS) were studied in slices from rat cerebral cortex incubated in the presence of inorganic [35S]sulfate. [35S]PAPS levels were directly evaluated after either isolation by ion-exchange chromatography or quantitative enzymatic transfer of its active [35S]sulfate group to an acceptor phenol under the action of added phenolsulfotransferase activity. [35S]PAPS formation was also indirectly followed by incubating slices in the presence of beta-naphthol and measuring the levels of [35S]beta-naphthyl sulfate ([35S]beta-NS). Whereas [35S]PAPS levels rapidly reached a plateau, [35S]beta-NS formation proceeded linearly with time for at least 1 h, an observation indicating that the nucleotide was continuously synthesized and utilized for endogenous sulfation reactions. [35S]PAPS formation in slices was completely and rather potently blocked by 2,6-dichloro-4-nitrophenol (IC50 = 10 microM), an inhibitor of the PAPS-synthesizing enzyme system in a cytosolic preparation. [35S]PAPS accumulation and [35S]beta-NS formation were strongly reduced by depolarizing agents such as potassium or veratridine. At millimolar concentrations, various excitatory amino acids (glutamate, aspartate, cysteate, quisqualate, and homocysteate) also elicited similar effects, whereas kainate and N-methyl-D-aspartate were inactive. This suggests that PAPS synthesis is turned off when cerebral cells are strongly depolarized.

Properties and localization of the sulfate-activating system in rat brain

The formation of the sulfate donor [35S]3'-phosphoadenosine 5'-phosphosulfate (PAPS) from inorganic [35S]sulfate was studied using a novel assay. The assay was based on the quantitative transfer of radioactivity from [35S]PAPS to beta-naphthol under the action of phenolsulfotransferase activity from rat brain cytosol, with the [35S]beta-naphthyl sulfate formed being isolated by polystyrene bead chromatography. This simple assay was validated by comparison of results with those derived from direct assay of [35S]PAPS isolated by either TLC or ion exchange chromatography. [35S]PAPS formation by a high-speed supernatant of rat cerebral cortex occurred with an optimal pH of approximately 7.6, varied linearly with time and protein concentration, and depended on the presence of Mg2+-ATP. The latter could not be replaced by other nucleotides such as GTP, UTP, or CTP, which at 1-5 mM concentrations inhibited the reaction. Mg2+ could not be replaced by Mn2+, which at micromolar concentrations inhibited the reaction. The apparent Km values of Mg2+-ATP (at 0.1 mM [35S]sulfate) and inorganic sulfate (at 5 mM Mg2+-ATP) were 2.7 and 0.2 mM, respectively. These kinetics parameters corresponded to those reported for purified ATP sulfurylase (EC 2.7.7.4), the enzyme responsible for the first step of PAPS synthesis in liver. The product of its reaction, [35S]adenosine 5'-phosphosulfate (APS), could not be detected after incubations, an observation implying that the action of APS kinase was not rate limiting in cerebral extracts tested under the selected experimental conditions. [35S]PAPS formation was detectable in cytosolic fractions from various brain regions, which displayed only limited differences in synthesizing activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Occurrence of phenolsulfotransferase in primary glial culture cells of rat

Phenolsulfotransferase (PST) activity towards phenol and monoamines was determined in rat brain and in primary cultures of rat astrocytes. The pH requirement, Km values and the proportion of PST activity with respect to phenol and dopamine as substrates were similar between PST from the glial cells and the rat cortex. The enzyme activity increased with age in the brain of older animals, and also with increasing incubation time in the primary culture of astroglia. The specific PST activity of the astroglia appeared to be higher than that of the brain enzyme. In glial cultures treated with 0.25 mM dibutyryl cyclic AMP in the same culture conditions, PST activity is suppressed to about 25% of its untreated counterpart, even though dibutyryl cyclic AMP at concentrations of ImM only slightly inhibited PST activity in vitro.

Conjugates of dopamine and serotonin in ventriculocisternal perfusates of the cat

The in vivo formation of acid-hydrolyzable conjugates of dopamine and of serotonin (presumably dopamine-O-sulfate and serotonin-O-sulfate) in ventriculocisternal perfusions of the cat is described. Small amounts of these amine conjugates were detected under quiescent conditions and during evoked release of the parent amines. The amounts of conjugated dopamine in perfusate were increased during and immediately after the period in which release of dopamine was evoked, but were not affected by inhibition of monoamine oxidase. In contrast, the efflux of serotonin conjugate during the evoked release of serotonin was not increased unless monoamine oxidase was inhibited. The data suggest that conjugation of amines in the CNS may be of functional importance in their disposition either under conditions of augmented release or during inhibition of oxidative deamination.

Sulfate conjugation of dopamine in rat brain: regional distribution of activity and evidence for neuronal localization

Brain tissue contains at least two forms of phenolsulfotransferase that are involved in the sulfate conjugation of biogenic amines and their metabolites. Two apparent Km values were obtained for p-nitrophenol at pH 7.4 (0.6 microM and 0.3 mM) but only one enzyme had the capacity to conjugate dopamine (Km = 130 microM). Dopamine sulfotransferase activity was found to vary 17-fold in different brain regions, with the highest levels in diencephalon, hippocampus, and striatum. To determine the cellular localization of the enzymes, phenolsulfotransferase activity was measured in striatum following selective destruction of striatal neurons by stereotaxic injection of 2 micrograms kainic acid. Fourteen days after injection the catecholamine sulfotransferase activity in the lesioned striatum was reduced to approximately 40-50% of that in the control contralateral striatum. There was a statistically significant correlation between the ratio of lesioned to control activity for the sulfotransferase and the neuronal marker enzymes glutamate decarboxylase and neuron-specific enolase. p-Nitrophenol sulfotransferase activity was also decreased in the lesioned striatum. These results suggest that PST activity is present within the kainic acid-sensitive neurons of the striatum. The regional variation in activity, together with the results of the kainic acid studies, suggest that sulfate conjugation of biogenic amines and their metabolites in brain may take place within specific types of neurons.

Conjugated dopamine in superfusates of slices of rat striatum

An acid-hydrolyzable conjugate of 3,4-dihydroxyphenylethylamine (dopamine, DA) was detected in superfusates from slices from rat striatum. The concentrations of endogenous free and conjugated DA, and of the acid metabolites (3,4-dihydroxyphenylacetic acid [DOPAC] and homovanillic acid [HVA]) in superfusates were measured using HPLC with electrochemical detection. Conjugated DA in superfusates represented 10-20% of the free DA under basal conditions and during release evoked by p-tyramine (5 X 10(-6) M to 5 X 10(-4) M); much smaller amounts of conjugated DA overflowed into superfusate when DA was released by equimolar concentrations of beta-phenylethylamine. Surprisingly, inhibition of monoamine oxidase by the inhibitors N-methyl-N-propargyl-3-(2,4-dichlorophenoxy)propylamine hydrochloride (clorgyline) or N-methyl-N-2-propynylbenylamine (pargyline) had little effect on the amounts of conjugated DA present in superfusate. Under basal conditions, the amounts of conjugated DA in superfusate were always less than the amounts of DOPAC but quite similar to the amounts of HVA. However, during release of DA evoked by p-tyramine the concentrations of conjugated DA in superfusate showed much more pronounced increases than those of the acidic metabolites.

Subcellular distribution of low- and high-molecular-weight acid phosphatases

Acid phosphatases (orthophosphoric-monoester phosphohydrolases (acid optimum), EC 3.1.3.2) of low and high molecular weight were separated by Sephadex G-75 filtration from extracts of rat brain, liver and kidney. The proportion of each phosphatase in the extract depends critically on the method employed for homogenate preparation, and no interconversion between high and low molecular weight forms was detected. In extracts obtained from subcellular organelles only high-molecular-weight acid phosphatase was detected, which is of lysosomal origin. Low-molecular-weight acid -phosphatase is restricted to the cell sap. Low- and high-molecular-weight acid phosphatases were characterized by their elution volumes, specific inhibition and activity with two substrates. It is suggested that the distribution pattern found om rat tissues could be common to all eukaryotic cells.