Phenacetin-N-deacetylase and its non-identity with the serotonin sensitive aryl acylamidase of brain

Inhibition of prostaglandin synthetases derived from neuronal and glial cells and rat renal medulla by ortho-, meta- and para-substituted aminophenolic compounds

Acetophenetidines, acetamidophenols, phenetidines and aminophenols substituted in o-, m- or p-position inhibit prostaglandin-synthetases originating from C 1300 mouse neuroblastoma cells (clone N2A), rat astrocytoma cells (clone C 6) and rat renal medulla. Desacetylated compounds were more potent inhibitors than their corresponding acetyl derivatives and many o- and m-analogues were more active than p-substituted structures like paracetamol (p-acetamidophenol) or phenacetin (p-acetophenetidine). When twelve o-, m- or p-aminophenolic test compounds were compared to acetylsalicyclic acid and indomethacin, o-, and p-phenetidine and o-aminophenol were as effective as acetylsalicyclic acid. All aminophenol derivatives which inhibited prostaglandin synthesis suppressed cultured nervous cell and kidney cyclo-oxygenases to similar extents. Our results suggest that aminophenolic drugs are not more effective against prostaglandin-synthetases in the CNS than against those in the periphery.

Serotonin-sensitive aryl acylamidase activity of platelet acetylcholinesterase

Serotonin-sensitive aryl acylamidase (AAA, EC 3.5.1.13) was purified to apparent homogeneity from sheep platelets by affinity chromatography and it was shown to be associated with the platelet acetylcholinesterase (AChE, EC 3.1.1.7). The basis for the association of the two enzymes was the following. Both enzyme activities co-eluted from the affinity columns with constant ratios of specific activities and percentage recoveries. Both enzymes co-migrated on gel electrophoresis. Both enzymes co-eluted during sepharose 6B gel filtration. Potent inhibitors of AChE such as bis(4-allyldimethyl ammoniumphenyl) pentan-3-one dibromide (BW 284C51), neostigmine and eserine also inhibited AAA potently. Both enzymes lost significant activity on treatment with deoxycholate or taurodeoxycholate and the loss could be partly restored by a mixture of phospholipids. The platelet AAA was specifically inhibited by serotonin and to a lesser extent by tryptamine but not by several other amines. It was also inhibited by acetylcholine and several of its analogues and homologues. It is suggested that in the platelets the two enzymes (AAA and AChE) are probably identical.

Inhibitory actions of desacetylation products of phenacetin and paracetamol on prostaglandin synthetases in neuronal and glial cell lines and rat renal medulla

The inhibitory actions of phenacetin and paracetamol and of their desacetylation products on prostaglandin synthesis were studied on enzyme preparations originating from a neuronal cell line (mouse neuroblastoma, clone N2A), a glial cell line (rat astrocytoma, clone C6) and rat renal medulla. All compounds tested inhibited cultured cell and kidney prostaglandin synthetases to similar extents. p-Phenetidine and p-aminophenol, the desacetylated metabolites of phenacetin and paracetamol, were either 7-10 times or 4 times more potent than paracetamol. Thus, p-Phenetidine inhibited prostaglandin synthesis as efficaciously as did acetylsalicylic acid. The possible roles of p-phenetidine as the active metabolite of phenacetin for cyclo-oxygenase inhibition in brain and of phenacetin as an organ pro-drug are discussed.

Brain aryl acylamidase

1. The serotonin (5-HT) sensitive brain aryl acylamidase (AAA) has received considerable attention due to its potential involvement in 5-HT action mechanism in CNS. 2. Multiple forms, AAA-1 and 2, have been separated by ammonium sulfate precipitation of brain extract and subsequent gel filtration. 3. Their chemical properties have been characterized and differentiated by effects of several classes of drugs including d-LSD, 5-HT, 5-HT related compounds and tetrahydro-beta-carbolines on their enzyme activities. 4. In the rat brain, AAA-1 shows highest specific activity in corpus striatum and lowest activity in cerebellum whereas AAA-2 shows highest specific activity in cerebellum and lowest activity in corpus striatum. 5. Subcellularly, AAA-1 exhibits highest specific activity in synaptosomal fraction of rat corpus striatum, lowest activity in mitochondrial fraction and no activity in nuclear fraction while AAA-2 exhibits highest specific activity in microsomal fraction and lowest activity in nuclear fraction. 6. Triton X-100 treatment altered the subcellular distribution pattern of both AAA-1 and AAA-2. 7. AAA-2 is possibly associated with true acetylcholinesterase (AChE) in brain based on its inhibition by neostigmine but its identity with AChE needs further elucidation. 8. To determine the physiological role(s) for brain AAA, naturally occurring aromatic alkylamines other than melatonin need to be tested as possible substrate(s) for the enzyme activity.

The identity of the serotonin-sensitive aryl acylamidase with acetylcholinesterase from human erythrocytes, sheep basal ganglia and electric eel

The identity of the serotonin-sensitive aryl acylamidase with acetylcholinesterase from three diverse sources, namely sheep basal ganglia, human erythrocyte membrane and electric eel, was examined. Both the enzymes co-purified with constant ratios of specific activity from all the three sources by different affinity chromatographic techniques. The ratio of acetylcholinesterase to aryl acylamidase activity was highest for basal ganglia, less for erythrocyte and lowest for eel enzymes. Both the purified enzymes co-migrated on polyacrylamide gel electrophoresis either as a single species or multiple species under different conditions. Gel density gradient electrophoresis indicated identical migration rates of both the enzymes. Extraction of the enzymes from the three sources by different techniques of membrane disruption and subsequent gel filtration on Sepharose 6B showed multiple peaks of enzyme activity. Both the enzymes had identical elution profiles on Sepharose 6B gel filtration. All the enzyme peaks from Sepharose 6B on gel electrophoresis showed co-migration of the enzyme activities. Apart from inhibition by serotonin and acetylcholine the purified aryl acylamidases from all the three sources were potently inhibited by neostygmine, eserine and BW 284C51, all strong inhibitors of acetylcholinesterase. It is suggested that the serotonin-sensitive aryl acylamidase is identical with acetylcholinesterase.