ANABAENA-FLOS-AQUAE AND OTHER CYANOBACTERIA POSSESS DIADENOSINE 5',5'''-P-1,P-4-TETRAPHOSPHATE (AP(4)A) PHOSPHORYLASE-ACTIVITY

Diadenosine 5',5triple prime-P-1,P-4-tetraphosphate (Ap(4)A) phosphory lase, previously only known in lower eukaryotes, has been detected in extracts of the cyanobacteria Anabaena flos-aquae, Anabaena variabilis and Synechococcus sp. The 32 kDa enzyme was partially purified from A . flos-aquae and separated from a 23 kDa hydrolytic activity. It had a pH optimum of 9.5 and required a bivalent cation of activity: Mg2+, M n2+, Ca2+, Co2+ or Zn2+. Diadenosine tri-, tetra- and penta-phosphates were all effective substrates (relative rates 0.85, 1.00 and 0.27 res pectively), while the hexaphosphate was a poor substrate and the dipho sphate was inactive. ADP was always one of the products of phosphoroly sis. Arsenate and vanadate could substitute for phosphate (relative ra tes 1.80, 2.25 and 1.00 respectively), but tungstate and sulphate coul d not. Chromate and molybdate were poor substrates. A search of the Ge nBank non-redundant database revealed a putative Ap(4)A phosphorylase gene in the cyanobacterium Synechocystis sp. The gene showed significa nt blocks of identity/similarity with yeast Ap(4)A phosphorylases I an d II, particularly the latter.