Isolation and substrate specificity of apurinic/apyrimidinic endonuclease from human placenta

A procedure for isolating electrophoretically homogeneous apurinic/apyrimidinic (AP) endonuclease from human placenta was elaborated. Enzyme preparations contained no impurities that cleave nucleic acids. The enzyme cleaves single-and double-stranded oligonucleotides lacking one or two bases. For a number of oligonucleotides containing one or two AP sites at various positions in one or both strands, K_M and V_max were estimated and their dependence on the position of AP site in the duplex was elucidated. Cleavage of single-stranded oligonucleotides also slightly depended on their nucleotide sequence and the position of AP site. Enzyme-induced active DNA conformation was assumed to be the major factor in the increased rate and the specificity of cleavage.