Pea chloroplast glyceraldehyde-3-phosphate dehydrogenase has uracil glycosylase activity

Pea (Pisum sativum) chloroplastic glyceraldehyde-3-P dehydrogenase (EC 1.2.1.13) was tested for uracil DNA glycosylase activity. It was found that both the chloroplast and the recombinant subunit B dehydrogenases remove uracil from poly(dA[3H]dU). The glycosylase activity of the recombinant subunit B enzyme and that of a truncated form corresponding in length to subunit A were associated with the dehydrogenase activity in gel-filtration experiments. Both activities of the chloroplast enzyme were inhibited by antisera raised against recombinant subunit B, and both activities of the recombinant subunit B enzyme were inhibited by antisera raised against pea chloroplast glyceraldehyde-3-P dehydrogenase. Antisera raised against Escherichia coli uracil glycosylase did not affect the glycosylase activity of the recombinant subunit B enzyme. The glycosylase pH activity profile of the chloroplast dehydrogenase was unique. It is distinct from the dehydrogenase pH activity profile and from the pH activity profiles of other plant glycosylases. The glycosylase activity, but not the dehydrogenase activity, of the recombinant subunit B enzyme was inhibited by uracil. Pyridine nucleotides stimulated the glycosylase activity. To our knowledge this is the first example of a nonhuman glyceraldehyde-3-P dehydrogenase, and of an NADP-dependent glyceraldehyde-3-P dehydrogenase, that exhibits uracil glycosylase activity.