title: A study of the binding of Mn2+ to bovine pancreatic deoxyribonuclease I and to deoxyribonucleic acid by electron paramagnetic resonance.
abstract: EPR studies of Mn2+ binding to bovine pancreatic deoxyribonuclease I show that the enzyme can bind three Mn2+ ions at pH 7.5 and 2 degrees. Two sites bind Mn2+ strongly, with a Kd of 10(-4)M, and the third binds Mn2+ weakly, with a Kd of 10(-3)M. Ca2+ competes with the two strong sites, whereas Mg2+ competes only with one of them, indicating that both sites are not equivalent. Mn2+ binding to DNA has been confirmed by EPR measurements. Two types of sites, with different affinities for Mn2+ binding, were found on DNA molecules, one with a Kd of 1.2 times 10(-4)M and the other with a Kd of 10(-3)M. Mg2+ ions can displace Mn2+ from the high affinity sites, but not from the low affinity sites. These results suggest the Mn2+ binds not only to the phosphate groups, but also to the electron donor groups of the base rings.
mesh_terms: D000818:Animals; D001665:Binding Sites; D002118:Calcium; D002417:Cattle; D004247:DNA; D003851:Deoxyribonucleases; D004578:Electron Spin Resonance Spectroscopy; D007700:Kinetics; D008274:Magnesium; D008345:Manganese; D010179:Pancreas / Q000201:enzymology*; D011485:Protein Binding; D011487:Protein Conformation; D013950:Thymus Gland
chemical_list: D008345:Manganese; D004247:DNA; D003851:Deoxyribonucleases; D008274:Magnesium; D002118:Calcium