[Purification and various properties of uracil-DNA-glycosylase from human placenta]

Uracil-DNA-glycosylase was isolated from human placenta and purified 2100-fold. The apparent Km value for non-methylated DNA substrate of the enzyme is 3.10(-7) M. However, Km for uracil-DNA-glycosylase was 3 times as low when methylated DNA was used as a substrate. It was shown that the initial rate of uracil excision was greater for the non-methylated than for the hypermethylated DNA. The experimental results indicate that the postreplicative methylation of DNA can interfere with uracil excision.