Purification and characterization of two exopolyphosphatases from the marine sponge Tethya lyncurium

Two exopolyphosphatases (exopolyphosphatase I and II; EC 3.6.1.11) which release orthophosphate from inorganic polyphosphates have been detected and purified for the first time from a marine sponge. Tethya lyncurium. Exopolyphosphatase I has a molecular mass of 45 kDa, a pH optimum of 5.0 and does not require divalent cations for activity, while exopolyphosphatase II has a molecular mass of 70 kDa, a pH optimum of 7.5 and displays optimal activity in the presence of Mg2+ ions. Final purification of the enzymes could be achieved by affinity chromatography on polyphosphate-modified zirconia. The mode of action of both enzymes was found to be processive. Orthophosphate is the sole product formed by exopolyphosphatase I, while degradation of linear polyphosphates by exopolyphosphatase II occurs to pyrophosphate as end product, which is hydrolyzed, if at all, only very slowly. Significant amounts of polyphosphate (approximately 30 micrograms/g wet weight) were found to be present in the sponge organism. Polyphosphate is shown to inhibit the formation of ATP by adenylate kinase activity present in T. lyncurium extracts in a competitive manner. The inhibitory effect of long-chain polyphosphates was higher than that of short-chain polyphosphate, suggesting a potential role of polyphosphate metabolism in regulating intracellular concentrations of adenylate nucleotides.