2 INTERNAL POOLS OF SOLUBLE POLYPHOSPHATE IN THE CYANOBACTERIUM SYNECHOCYSTIS SP. STRAIN PCC-6308 - AN IN-VIVO P-31 NMR SPECTROSCOPIC STUDY

Two intracellular pools of soluble polyphosphate were identified by in vivo P-31 NMR spectroscopy in the cyanobacterium Synechocystis sp. st rain PCC 6308. Polyphosphate was present in the cells after growth in sulfur-limited media containing excess phosphate. The presence of poly phosphate was confirmed by transmission electron microscopy and chemic al analysis. P-31 NMR spectroscopy of whole cells treated with EDTA re vealed two pools of mobile polyphosphate. A downfield shift and narrow ing of part of the broad polyphosphate resonance was observed after ED TA treatment, suggesting that EDTA binds metal ions normally associate d with some of the polyphosphate. Phosphate, but not polyphosphate, le aked out of the cells after this treatment. Addition of magnesium ions caused the downfield shift in the polyphosphate resonance to move bac k toward its original value. These data show that only part of the cat ion-complexed polyphosphate is accessible to the added EDTA and sugges t that there are two internal fractions of NMR-visible polyphosphate i n the cells, only one of which loses its associated cations to EDTA. S pheroplast formation showed that polyphosphate was not present in the periplasm of the cells.