Pergamon 0031-9422(95)00007-0 Phytochemistry, Vol. 39,No.4, pp. 771-774, 1995 Copyright© 1995 Elsevier Science Ltd Printedin GreatBritain. Allfights reserved 0031-9422/95 $9.50 + 0.00 BIOSYNTHESIS OF THE HETEROCYST GLYCOLIPIDS IN THE CYANOBACTERIUM ANABAENA CYLINDRICA* AGATAGAMBACORTA, ANNUNZIATA SORIENTE,~ ANTONIO TRINCONEand GUIDO SODANOt~ Istituto per la Chimica M.I.B., CNR, Via Toiano 6, 80072 Arco Feliee (NA), Italy; ~'DipartimenIodi Chimica, Universitfi di Salerno, 84081 Baronissi (SA), Italy (Received in revisedform 2 November 1994) Key Word Index--Anabaena cylindrica; Cyanobacteria; heterocyst glycolipids; biosynthesis. Abstract--Incorporation of [ 1-13 C] acetate into the heterocyst glycolipids of the cyanobactcrium A nabaena cylindrica indicated that (i) the long chain of the aglyconcs originates from a de novo biosynthesis and not by elongation of a preformed shorter molecule and that (ii) there is no apparent interconversion between the hydroxyketone and alcohol glucosides. INTRODUCTION The site of nitrogen fixation in certain filamentous cya- nobacteria resides in specialized cells called heterocysts which originate by differentiation of vegetative cells under aerobic conditions and in the absence of nitrogen salts. The heterocysts have a thick envelope containing a laminated layer of glycolipids and an outer homogenous layer of polysaccharide [ 1]. According to several authors [2, 3], the thick envelope plays a role in the protection of the enzyme nitrogenase from oxygen, restricting air diffu- sion to a level which allows sufficient nitrogen penetra- tion while maintaining oxygen diffusion to a level which can be removed by respiratory scavenging. *Part 4 in the series 'The Heterocyst Glycolipids of Cyan- obacteria'. For previous papers in the series see refs [6-8]. ~Author to whom correspondence should be addressed. The glycolipids constituting the laminated layer are unique to nitrogen-fixing cyanobacteria [4, 5] and their structures have only recently been fully elucidated in certain cyanobacteria [6, 7], including Anabaena cylin- drica [8]. From the latter, 1-4 were isolated, the major being 3 and 1. In particular, 3 seemed the most wide- spread heterocyst glycolipid in cyanobacteria. The biosynthesis of the heterocyst glycolipids in A. cylindrica has also been previously investigated [9-11]. In the previous studies, sodium [1-14C] acetate was used as precursor and the incorporation in the whole com- pounds was considered, no attempts having been made at localizing the label on the individual carbon atoms. The authors concluded that the activity of key enzymes involved in the biosynthesis of the heterocyst glycolipid fraction is stimulated during heterocyst differentiation and that in mature heterocysts the formation of the characteristic very long chain essentially ceases. Some H0 HO'~___ 0 HO-.~ ~ ~ HO- "~ 0 O_H 1 3 771 H0 HO ~,~ 0 OH OH 2 HO _OH _OH _OH (