SOME PROTEIN PROPERTIES IMPORTANT FOR ENZYME CATALYSIS - New Trends in Enzyme Catalysis and Biomimetic Chemical Reactions - page 156

The region of the cytochrome c active center is surrounded by a cluster of positively
charged lysine residues. The existence of such a structural moiety is the basis for the
specific affinity of this electron carrier to cytochrome c oxidase. However, in spite of
this, our experiment did not locate significant local electrostatic charges on the protein
interface in the vicinity of the heme group at pH 10.7 (isoelectric point) or pH 7 with an
ionic strength of 0.09 M (Table 4.2.). Therefore, while the charged lysine
groups of cytochrome c contribute significantly to the direct electrostatic interaction with
the surface of cytochrome c oxidase, they apparently do not induce a markedly positive
charge on the hemin. The existence of a large positive charge in this region could
prevent electron transfer from cyt c.
While the differently charged spin-probes have only been used so far on a rather
limited number of examples reported herein, the results show that these new
methodologies hold great promise for the investigation of local electrostatic fields in a
wide range of biologically significant molecules.
A similar approach was employed in Hecht et al. (1995) for determining the
electrostatic potential near the surface of calf thymus DNA. Spin-spin interaction
between an derivative of 9-aminoacridine attached to DNA and free
labeled nitroxides of different charges was monitored by electron-electron double
resonance (ELDOR). The electrostatic potential near the surface of DNA was calculated
using a nonlinear Poisson-Boltzman equation. The calculated results agreed with the
experimental potentials.
The effect of dipole-dipole interaction between the heme group of myoglobin
and water protons was used to study heme hydration and displacement in the pre-
denaturational conformational transition of the molecule (Derzhansci et al. 1970).