BIOGELS OF CYTOCHROME-C - CYTOCHROME-C PEROXIDASE COMPLEX STUDIED BY ELECTRON-PARAMAGNETIC-RESONANCE SPECTROSCOPY

Cytochrome c : cytochrome c peroxidase (Cc : CcP in 1 : 1 ratio) compl ex was successfully encapsulated in sol-gel derived glass. The electro n paramagnetic resonance (e.p.r.) and optical absorption techniques we re used to characterize the coordination number, spin state, charge-tr ansfer activity and structural orientation of Cc : Cc complex and its constituents. The sol-gel encapsulation of metalloproteins allows, for the first time, the detection of e.p.r. signals of biological systems at room temperature. CcP exhibits an e.p.r. spectrum representing the high spin and purely axial symmetry with parameters at g(perpendicula r to) congruent to 6 and g(parallel to) congruent to 2 and an electron ic absorption spectrum with a descent in spectral intensity of shoulde r band at 380 nm and a blue-shifted charge-transfer band at 620 nm. Cc shows an e.p.r. spectrum characterizing a mixture of high spin (g(per pendicular to) congruent to 6 and g(parallel to) congruent to 2) and l ow spin (g(x) = 2.7, g(y) = 2.2 and g(z) = 1.8) components. Upon compl exation, Cc :CcP pair displays a single and broad e.p.r. spectrum at g (parallel to) congruent to 2 and a light absorption spectrum with a re d-shifted Soret band at 423 nm, a blue-shifted charge-transfer band at 620 nm and an intensified charge-transfer band at 507 nm. These resul ts suggest that the sol-gel encapsulated Cc:CcP complex has the follow ing chemical and physical characteristics: (a) a hexa-coordination, (b ) a high-spin state, (c) an active charge-transfer (or redox) pair, an d (d) the direction of the g(parallel to) paramagnetic center of Cc : CcP complex lies nearly parallel to that of the heme normal. The struc tural coordinations of the sol-gel encapsulated Cc, CcP and Cc:CcP are examined. Moreover, the possible use of biogels at the sol, gelation, and xerogel stages during gel processing to control the structural ri gidity and spatial separation/orientation of the encapsulated heme pro teins and to study their possible routes of long-range electron transf er reactions are also discussed.