Study of polyphosphate metabolism in intact cells by 31-P nuclear magnetic resonance spectroscopy.

Inorganic polyphosphates (polyp) are naturally occurring linear polymers of orthophosphate that are found in microorganisms, lower eukaryotes such as yeast, and animals (Harold 1966, Kulaev and Vagabov 1983; Wood and Clark 1988). In certain cases, polyp can accumulate to more than 10% of total dry mass. The ubiquitous presence of polyp suggests that they may have important physiological functions. For example, polyp has been proposed to function as a high-energy reserve or a phosphate reserve and may play an important role in regulating the levels of ATP (Harold 1966). Due to their polyanionic nature, polyp can also serve as counter ions for cationic species such as Mg2+, Mn2+, basic amino acids, and polyamines. In this regard, they may function in counteracting the osmotic pressure exerted by basic amino acids and various cations accumulated in fungal vacuoles. In addition, the presence of polyp in nuclei and membrane in certain organisms would suggest that polyp may have other unknown functions. It has been difficult to study the metabolism, regulation, and function of polyp for the following reasons: (1) polyp does not possess chromophores in its chemical structures; (2) polyp cannot easily be derivatized with specific chromophore or fluorescent probe; and (3) polyp may exist as a mixture of polymers with varying chain length, ranging from 3 to 1000 residues. Several analytical methods have been developed to study polyp, including enzymatic assay, HPLC and electrophoresis (reviewed by Wood and Clark 1988). Among them, in vivo phosphorus-31 nuclear magnetic resonance ( 3 1 ~ NMR) remains, arguably, the unique one, being the least disruptive and quantitative (Roberts 1987). In vivo NMR is a rapid and non-invasive technique suitable for studying metabolic processes in intact cells, tissues, and organelles. High resolution 3 1 ~ ~ ~ ~ has provided valuable information on the identification and quantitation of phosphorus metabolites, on the intracellular pH and compartmentation, and on the kinetics and pathways of biochemical reactions. The