Polyphosphate-hydrolysis--a protective mechanism against alkaline stress?

Different microorganisms, including yeast and algae, accumulate large amounts of polyphosphates. However, the physiological role of polyphosphates is largely unknown. In vivo 31P NMR studies, carried out in the unicellular alga, Dunaliella salina, demonstrate the cytoplasmic alkalization induces massive hydrolysis of polyphosphates, which is correlated kinetically with the recovery of cytoplasmic pH. Analysis of acid extracts of the cells indicates that long-chain polyphosphates are hydrolysed mainly to tripolyphosphate. It is suggested that the hydrolysis of polyphosphates provides a pH-stat mechanism to counterbalance alkaline stress.