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) complex was successfully encapsulated in sol-gel derived glass. The electron paramagnetic resonance (e.p.r.) and optical absorption techniques were used to characterize the coordination number, spin state, charge-transfer 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(perpendicular to) congruent to 6 and g(parallel to) congruent to 2 and an electronic absorption spectrum with a descent in spectral intensity of shoulder 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(perpendicular to) congruent to 6 and g(parallel to) congruent to 2) and low spin (g(x) = 2.7, g(y) = 2.2 and g(z) = 1.8) components. Upon complexation, 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 red-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 results suggest that the sol-gel encapsulated Cc:CcP complex has the following chemical and physical characteristics: (a) a hexa-coordination, (b) a high-spin state, (c) an active charge-transfer (or redox) pair, and (d) the direction of the g(parallel to) paramagnetic center of Cc : CcP complex lies nearly parallel to that of the heme normal. The structural 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 rigidity and spatial separation/orientation of the encapsulated heme proteins and to study their possible routes of long-range electron transfer reactions are also discussed.