Observations on the pyridoxal 5'-phosphate inhibition of DNA polymerases

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Abstract
Pyridoxal 5''-phosphate at concentrations > 0.5 mM inhibits polymerization of deoxynucleoside triphosphate catalyzed by a variety [avian myeloblastosis virus, Rauscher leukemia virus, simian sarcoma virus, feline leukemia virus, Wistar rat embryo fibroblast type C virus, Mason Pfizer virus, mouse mammary tumor virus, HeLa cell and Escherichia coli] of DNA polymerases. The requirement for a phosphate and aldehyde moiety of pyridoxal phosphate for inhibition to occur is clearly shown by the fact that neither pyridoxal nor pyridoxamine phosphate are effective inhibitors. Since the addition of nonenzyme protein or increasing the amount of template primer exerted no protective effect, there appears to be specific affinity between pyridoxal phosphate and polymerase protein. The deoxynucleoside triphosphates could reverse the inhibition. The binding of pyridoxal 5''-phosphate to enzyme appears to be mediated through classical Schiff base formation between the pyridoxal phosphate and the free amino group(s) present at the active site of the polymerase protein. Inhibition by pyridoxal phosphate is competitive with respect to substrate deoxynucleoside triphosphate(s).

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