Inactivation of avian myeloblastosis virus DNA polymerase by specific binding of pyridoxal 5'-phosphate to deoxynucleoside triphosphate binding site.

Avian myeloblastosis virus (AMV) DNA polymerase is inactivated by preincubation with pyridoxal 5'-phosphate. This inactivation is relatively specific since various pyridoxal-5'-P analogs cause no inactivation. This effect is reversible but can be made irreversible by reduction with sodium borohydride; the reduced pyridoxal-5'-P adduct exhibits a new absorbance maximum at 325 nm and a fluorescence emission at 392 nm when excited at 325 nm. The evidence presented suggests the formation of a Schiff base between pyridoxal-5'-P and a nucleophilic residue of AMV DNA polymerase. The presence of a deoxynucleoside 5'-triphosphate (dTTP) protected the enzyme from inactivation. Reduction of the pyridoxal-5'-P enzyme complex in the presence or absence of a deoxynucleoside 5'-triphosphate showed that the alpha subunit possesses five reactive amino groups, one of which is essential for catalytic activity; the beta subunit has three reactive amino groups which are not involved in the deoxynucleoside binding site.