title: Interaction of zinc ions with DNA-dependent RNA polymerases A, B and C isolated from calf thymus.
abstract: Purified DNA-dependent RNA polymerases A, B and C isolated from calf thymus contain a significant amount of zinc. Atomic absorption spectroscopy revealed the presence of 6.7, 5.35 and 2.6--4.1 g-atoms of zinc per mole of polymerase A, B and C, respectively. These enzymes are inhibited by treatment with 1,10-phenanthroline at concentrations varying from 10(-5) to 10(-4) M. However, the addition of zinc ions does not restore fully the activity of 1,10-phenanthroline treated enzymes. Exogenous zinc ions reduce in vitro an overall RNA synthesis catalysed by RNA polymerases from calf thymus. In addition to the sites which bind zinc in a specific and stoichiometric way these enzymes possess other classes of binding sites with high and low affinity. Occupancy by exogenous zinc of these additional binding sites inhibit polymerase activity.
mesh_terms: D000818:Animals; D002417:Cattle; D012321:DNA-Directed RNA Polymerases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D046911:Macromolecular Substances; D008970:Molecular Weight; D010618:Phenanthrolines / Q000494:pharmacology; D013054:Spectrophotometry, Atomic; D013950:Thymus Gland / Q000201:enzymology*; D015032:Zinc / Q000032:analysis / Q000494:pharmacology*
chemical_list: D046911:Macromolecular Substances; D010618:Phenanthrolines; D012321:DNA-Directed RNA Polymerases; D015032:Zinc; C025205:1,10-phenanthroline