Serotonin-sensitive aryl acylamidase activity of platelet acetylcholinesterase

Abstract

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.