An ESR Study of the Mn(II)-Heavy Meromyosin System

Abstract

The Mn(II)-heavy meromyosin system was studied by measuring the ESR spectrum of Mn(II). The temperature dependence of the line width parameter W(1, t) of a freshly prepared sample changes at around 7-10 degrees C, where W(1, t) is the reciprocal of the peak-to-peak height of the lowest magnetic field component of the hyperfine structure. It is shown that the change in the slope of W(1, t) at 7-10 degrees C is due to a change in the structure of Mn(II)-heavy meromyosin or a change in the interaction between Mn(II) and heavy meromyosin without ATP. This result is in accord with the recently reported observations that heavy meromysin ATPase activity showed different temperature dependence above and below 10 degrees C in the presence of Mn(II). The characteristics of the spectrum of the Mn(II)-heavy meromyosin system in the liquid state between 2 degrees C and 20 degrees C are compared with those of a frozen sample of Mn(II)-heavy meromyosin in a low temperature region (-50-0 degrees C) and with those of the lyophilized material. The forbidden transitions are observed, and hence the zero field splitting parameter can be obtained. It is 115 +/- 15 gauss at -50 degrees C, and decreases with increase of the temperature to 70 +/- 15 gauss at 20 degrees C.

Experimental evidence for asymmetrical shielding of nucleosomal DNA by histones

“…It is now well known that Mn (II) binds to DNA through a chelation process between a phosphate group and the N7 of the guanine (10) and such a binding indicates the existence of an outside site for Mn (II) as has been shown by proton relaxation enhancement studies (11,12). As Mn (II) is a paramagnetic ion, it is possible to use electron paramagnetic resonance (EPR) as a tool for studies on its interactions with biological macromolecules like proteins, nucleotides, nucleic acids (13)(14)(15)(16)(17).…”