JBC, Vol. 250, Issue 17, 6631-6635, Sep, 1975
A study of the binding of Mn2+ to bovine pancreatic deoxyribonuclease I and to deoxyribonucleic acid by electron paramagnetic resonance
H. Jouve, H. Jouve, E. Melgar and B. Lizarraga
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.