Mechanistic studies on E. coli DNA topoisomerase I: Divalent ion effects

Journal Article · Wed May 01 04:00:00 EDT 1991 · Journal of Inorganic Biochemistry; (United States)

DOI:https://doi.org/10.1016/0162-0134(91)80035-G· OSTI ID:5388084

Domanico, P L; Tse-Dinh, Y C ^[1]

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1. Department of Enzymology, Glaxo Research Laboratories, Research Triangle Park, NC (USA)

E. coli DNA topoisomerase I catalyzes the hydrolysis of short, single stranded oligodeoxynucleotides. It also forms a covalent protein-DNA complex with negatively supercoiled DNA in the absence of Mg2+ but requires Mg2+ for the relaxation of negatively supercoiled DNA. In this paper we investigate the effects of various divalent metals on catalysis. For the relaxation reaction, maximum enzyme activity plateaus after 2.5 mM Mg2+. However, the rate of cleavage of short oligodeoxynucleotide increased linearly between 0 and 15 mM Mg2+. In the oligodeoxynucleotide cleavage reaction, Ca2+, Mn2+, Co2+, and Zn2+ inhibit enzymatic activity. When these metals are coincubated with Mg2+ at equimolar concentrations, the normal effect of Mg2+ is not detectable. Of these metals, only Ca2+ can be substituted for Mg2+ as a metal cofactor in the relaxation reaction. And when Mg2+ is coincubated with Mn2+, Co2+, or Zn2+ at equimolar concentrations, the normal effect of Mg2+ on relaxation is not detectable. The authors propose that Mg2+ allows the protein-DNA complex to assume a conformation necessary for strand passage and enhance the rate of enzyme turnover.

• OSTI ID: 5388084
• Journal Information: Journal of Inorganic Biochemistry; (United States), Journal Name: Journal of Inorganic Biochemistry; (United States) Vol. 42:2; ISSN JIBID; ISSN 0162-0134
• Country of Publication: United States
• Language: English

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ALKALINE EARTH METAL COMPOUNDS
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