Substrate specificity of phenol sulfotransferase from primary cultures of bovine brain microvessel endothelium

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Abstract
The substrate specificity of the thermostable phenol sulfotransferase (PST) from primary cultures of brain microvessel endothelial cell monolayers was characterized. Selected catecholamines, catecholamine metabolites, and p-nitrophenol at 5, 50, and 500 μM were used as substrates in PST assays of cytosol extracts. Endogenous catecholamines, epinephrine, norepinephrine, and dopamine, exhibited no detectable activity as substrates (500 μM) compared to 500 μM p-nitrophenol as substrate (1.8 pmol/mg/min specific activity) for the PST. In contrast, 500 μM of either deaminated or 3-O-methylated metabolites of catecholamines exhibited intermediate (≈1.0 pmol/mg/min specific activity) to low (≈0.2 pmol/mg/min specific activity) activity, respectively, as substrates compared to p-nitrophenol as substrate for the PST. Additionally, 500 μM of metabolites of catecholamines that were both deaminated and 3-0-methylated exhibited high activity (>3.0 pmol/mg/min specific activity) as substrates compared top-nitrophenol as substrate for the PST. Qualitatively similar results were observed at lower substrate concentrations. Therefore, results from this study suggest a potential role for PST as part of the “enzymatic” blood-brain barrier in regulating transendothelial passage of endogenous catecholamines between the blood and the brain.