0041_0101@4Mo153-7 Toxim~, Vol. 33. No. 2. pp. 133-142. 1995 Copyright 0 1995 Elsevler Science Ltd Printed in Great Britain. All rinhts reserved . , 004-0101/95‘$9.50 + 0.00 INHIBITION OF ACETYLCHOLINESTERASE BY A PSEUDOZOANTHOXANTHIN-LIKE COMPOUND ISOLATED FROM THE ZOANTHID PARAZOANTHUS AXINELLAE (0. SCHMIDT) TOM TURK,’ PETER MACEK’ and DUSAN SUPUT’ ‘Department of Biology, Biotechnical Faculty, University of Ljubljana, V&na pot 111, P.O.B. 486, 61000 Ljubljana, Slovenia; and *Institute of Pathophysiology, Medical Faculty, University of Ljubljana, 61105 Ljubljana, Slovenia (Received 3 June 1994; accepted 11 September 1994) T. Turk, P. MaEek and D. Suput. Inhibition of acetylcholinesterase by a pseudozoanthoxanthin-like compound isolated from the zoanthid Paruzoan- rhus axinelfae (0. Schmidt). Toxicon 33, 133-142, 1995.-An ethanolic extract from a zoanthid crust coral Purazoanthus axinellae was lethal to mice and crabs and exhibited anticholinesterase activity. The isolation of several AChE inhibitors with the aid of RP-HPLC is described. The most abundant of the inhibitors present in the P. axinellae extract was identified as pseudozoanthox- anthin or an almost identical compound which belongs to the chemically well-characterized series of tetrazacyclopentazulene natural pigments from the genera Parazoanthus, Epizoanthus, Zoanthus and Palythoa. The inhibitor has a mol. wt of 242 and acts as a competitive inhibitor with a Ki of 4pM. The inhibitor exhibited a strong blue fluorescence. In vivo action of crude extract and the isolated inhibitor showed a typical picture of systemic acetylcholinester- ase inhibition. Atropinization of experimental animals prior to injection of the inhibitor almost entirely neutralized its activity. INTRODUCTION The zoanthid crust coral, Purazounthus uxinellae (0. Schmidt), inhabits underwater caves and crevices of the Mediterranean Sea, usually associated with sponges belonging to the family Axinellidae. So far, P. axinellae has been a source of yellow, fluorescent tetrazacy- clopentazulene pigments known as zoanthoxanthins, parazoanthoxanthins and pseudo- zoanthoxanthins (Cariello et al., 1974a-c, 1979). Related pigments, palyzoanthoxanthins, were also isolated in minute amounts from two Pulythoa species (Cariello et al., 1979). In Parazoanthus gracilis, the pseudozoanthoxanthin type compound paragracine was found (Komoda et al., 1975). Although chemically well characterized, the biological activity of these pigments has scarcely been studied. Around 280 PM, zoanthoxanthin has been reported to inhibit uncompetitively mitochondrial succinic oxidase (Cariello and Tota, 1974) while 40 ,u M was cytotoxic in vitro (Jimenez and Crews, 1993). Paragracine possessed histamine and papaverine-like pharmacological activity (Komoda et al., 1975). It also blocked nerve membrane sodium channels in a current-dependent manner (Seyama et al., 1980). 133