Enzymes of Polyphosphate Biosynthesis

The reaction of reverse transfer of energy-rich phosphate residues from ATP to PolyPs and from PolyPs to ADP, thus linking energy-rich pools, was discovered by Kornberg and co-workers (Kornberg el al., 1956 Kornberg, 1957 a,b)  

The enzyme was partly purified from Propionibacterium shermanii (Robinson et al., 1987), and was shown to be a monomeric enzyme with a molecular mass of 83 kDa. It was demonstrated that short-chain PolyPs of 6-80 residues serve as primers for the synthesis of long-chain PolyPs using ATP by a strictly processive mechanism. The largest PolyPs synthesized was PolyP75o. 

The Biochemistry of Inorganic Polyphosphates I. S. Kulaev, V. M. Vagabov and T. V. Kulakovskaya 2004 John Wiley Sons, Ltd ISBN 0-470-85810-9 

Polyphosphate kinase was purified from Acinetobacter sp. (Trelstad et al., 1999). It was a 79 kDa monomer. In contrast to the E. coli enzyme, the polyphosphate kinase purified from this bacterium seems to work only in the forward direction, i.e. it produces but does not degrade PolyPs. 

In many bacteria, polyphosphate kinase is the main enzyme of PolyP metabolism. This was confirmed by a sharp decrease of PolyP content in ppkl mutants of E. coli (Crooke etal, 1994 Rao and Kornberg, 1996 Rao et al., 1998), N. meningitidis (Tinsley and Gotschlich, 1995), and V. cholerae (Ogawa et al., 2000b). 

---

Little is known of the ways of biosynthesis and insertion in the membranes of PolyP-PHB-Ca2+ complexes. In polyphosphate kinase 1 mutants of E. coli, the amounts of the complexes did not change (Castuma et al., 1995). Therefore, the PolyP in the complexes is synthesized not by polyphosphate kinase 1 but by another enzyme. E. coli strain, which lacks the AcrA component of a major multi-drug resistance pump, had greatly reduced amounts of the complexes and was defective in its ability to maintain sub-micromolar levels of free Ca2+ in the cytoplasm (Jones et al., 2003). This indicates that the AcrAB transporter may have a novel, hitherto undetected, physiological role, either directly in the membrane assembly of the PHB complexes or the transport of a component of the membrane, which is essential for assembly of the complexes into the membrane. 

---