The effect of temperature on the spectroscopic properties of the heme c octapeptide from cytochrome c.

The effect of temperature on the optical properties of the acetylated heme c octapeptide from cytochrome c was examined. At above ambient temperatures the observed optical spectrum with maxima at 549 and 424 nm was characteristic of high-spin ferrous hemeproteins. At below ambient temperatures the optical spectrum became characteristic of low-spin ferrous hemeproteins with maxima at 547, 518, and 410 nm. A thermodynamic characterization of this two component system yielded a deltaHO of -10.1 +/- 0.7 kcal/mol and a delta S0 of-37.6 +/- 2.5 e.u. for the temperature dependent process. Discussion of the spectroscopic and thermodynamic parameters was presented in terms of the consistent magnetic and structural properties of heme complexes.