Essential for rapid growth and for sporulation. Catalyzes the interconversion of 2-phosphoglycerate (2-PGA) and 3-phosphoglycerate (3-PGA). (2R)-2-phosphoglycerate = (2R)-3-phosphoglycerate Binds 2 manganese ions per subunit. Could be inhibited during sporulation by acidification of the forespore, thus allowing accumulation of the spore's large depot of 3-phosphoglyceric acid. Very sensitive to pH. The enzyme activity rises 25-fold between pH 6 and 8. Addition of manganese increases the thermal stability. Carbohydrate degradation; glycolysis; pyruvate from D-glyceraldehyde 3-phosphate: step 3/5. Monomer. The pH sensitivity is physiologically relevant, since it allows for the regulation of iPGM activity during different parts of the developmental cycle. Belongs to the BPG-independent phosphoglycerate mutase family.