title: Mechanism of the idling-turnover reaction of the large (Klenow) fragment of Escherichia coli DNA polymerase I.
abstract: The mechanism of the idling-turnover reaction catalyzed by the large (Klenow) fragment of Escherichia coli DNA polymerase I has been investigated. The reaction cycle involved is one of excision/incorporation, in which the 3' deoxynucleotide residue of the primer DNA strand is partitioned into its 5'-mono- and 5'-triphosphate derivatives, respectively. Mechanistic studies suggest the 5'-monophosphate product is formed in the first step by simple 3'----5' exonucleolytic cleavage. Rapid polymerization follows with the concomitant release of inorganic pyrophosphate. In the second step, the 5'-triphosphate product is generated by a pyrophosphorolysis reaction, which, despite the low concentration of pyrophosphate that has accumulated, occurs at a rate that is comparable with that of the parallel 3'----5' hydrolysis reaction.
mesh_terms: D004256:DNA Polymerase I / Q000378:metabolism*; D003838:Deoxyadenine Nucleotides / Q000378:metabolism; D003848:Deoxyguanine Nucleotides / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology*; D007700:Kinetics; D010446:Peptide Fragments / Q000378:metabolism*
chemical_list: D003838:Deoxyadenine Nucleotides; D003848:Deoxyguanine Nucleotides; D010446:Peptide Fragments; D004256:DNA Polymerase I