- DNA polymerases catalyze the 3′–5′-pyrophosphorolysis of a DNA primer annealed to a DNA template in the presence of pyrophosphate (PPi). In this reversal of the polymerization reaction, deoxynucleotides in DNA are converted to deoxynucleoside 5′-triphosphates. Based on the charge, size, and geometry of the oxygen connecting the two phosphorus atoms of PPi, a variety of compounds was examined for their ability to carry out a reaction similar to pyrophosphorolysis. We describe a manganese-mediated pyrophosphorolysis-like activity using pyrovanadate (VV) catalyzed by the DNA polymerase of bacteriophage T7. We designate this reaction pyrovanadolysis. X-ray absorption spectroscopy reveals a shorter Mn-V distance of the polymerase-VV complex than the Mn-P distance of the polymerase-PPi complex. This structural arrangement at the active site accounts for the enzymatic activation by Mn-VV. We propose that the Mn2+, larger than Mg2+, fits the polymerase active site to mediate binding of VV into the active site of the polymerase. Our results may be the first documentation that vanadium can substitute for phosphorus in biological processes.