Cytochrome c: electron emission, photodegradation and mutual interaction with vitamin C.

Cytochrome c (Cytc) in airfree, aqueous media (pH ~7.4; 37°C) can emit e(-)(aq) when exited in single state by monochromatic UV light (λ=254 nm). The obtained Qi(e(-)(aq)) at lower Cytc concentrations is higher compared to the amount obtained at higher substrate concentrations because at >10(-8) mol l(-1) Cytc 'associates' (unstable complexes) are formed, which consume a part of the ejected e(-)(aq). The primary, as well as secondary, photolytic products of the substrate likewise emit e(-)(aq), but with much lower Qi(e(-)(aq)) values. On the other hand, the photolysis Q(Cytc) values are lower than those of Qi(e(-)(aq)), since Cytc transients can be regenerated by partial consumption of emitted e(-)(aq). In addition to this, the produced Cytc(•+) (radical cations) can react with water, thus also regenerating Cytc.