METACHROMATIC GRANULES OF MICROORGANISMS

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Abstract
Lipids are a major component of the volutin granule. These lipids are loosely bound to or overlaid with protein. Other components include ribonucleic acid, probably linked to the protein, and energy-rich polyphosphates. These polyphosphates may be complexed with the ribonucleic acid through a divalent cation such as Mg++. The various functions ascribed to volutin are reviewed. The simultaneous occurrence of lipid and high-energy phosphate in a discrete well-organized granule which apparently arises de novo indicates a common precursor substance. Under anaerobic conditions, or after phosphate starvation and subsequent feeding, it is hypothesized that 2-phosphoenolpyruvate furnishes both high-energy phosphate and, after decarboxylation, "active acetate" for lipid synthesis. Pyrophosphate, split out during lipid synthesis, acts as "primer" in the reaction adenosine triphosphate (ATP) + phosphate primeradenosine diphosphate (ADP) + polyphosphate. Phosphoenolpyruvate may accumulate during a time of nutrient imbalance when the rate of phosphate cycline from 1,3-diphosphoglyceric acid to ADP exceeds the rate from phosphoenolpyruvate to ADP and all newly formed ATP is channeled toward exterification of hexose. Addition of ADP would therefore restore balance and inhibit volutin formation.