Phosphopentomutase

Phosphopentomutase is an enzyme that catalyzes the reversible intramolecular transfer of a phosphate group within pentose phosphates, interconverting ribose-1-phosphate and ribose-5-phosphate. This reaction links ribose salvage pathways to the pentose phosphate pathway, supplying ribose-5-phosphate for nucleotide biosynthesis and central metabolism.

Like other enzymes in the alpha-D-phosphoglucomutase/phosphomutase superfamily, phosphopentomutase operates via a covalent phosphoserine intermediate and requires a divalent metal ion, typically Mg2+ or Mn2+, for activity. The catalytic serine in the active site is temporarily phosphorylated by the substrate, enabling intramolecular phosphate transfer and regeneration of the active site phosphate for subsequent turnover.

Structurally, phosphopentomutase is usually a soluble cytosolic enzyme of roughly 450–500 amino acids and adopts a four-domain architecture characteristic of the mutase family. The active-site serine lies within a conserved sequence motif and coordinates substrate binding and phosphate transfer, with the reaction proceeding through domain movements that reposition the phosphate group.

Biological role and occurrence: phosphopentomutase is found in bacteria and other organisms where pentose catabolism or nucleotide degradation provides ribose-1-phosphate that must be converted to ribose-5-phosphate. In bacteria such as Escherichia coli, the enzyme contributes to ribose salvage and integration with the pentose phosphate pathway, supporting nucleotide turnover and energy metabolism. The enzyme is studied for its catalytic mechanism, substrate specificity, and its relationship to other sugar-phosphate mutases within the same superfamily.