Heme-Linked Properties of <em>Euglena</em> Cytochrome <em>f</em>.

Oxidized Euglena cytochrome ƒ has an absorbance band at 695 nm which disappears upon reduction. Various treatments that cause known changes of conformation of cytochrome c appear to have similar effects on cytochrome ƒ Heating cytochrome ƒ results in the gradual disappearance of the 695-nm band; the thermodynamic parameters for this change of the tertiary structure at 26 &#176;C and ionic strength 0.01 are: ΔF= +2.67 kcal/mole, ΔH= +33 kcal/mol and ΔS = + 102 cal &#215; K-1 &#215; mol-1. The pK values obtained by equilibrium titrations of the herne-linked acid and alkaline ionizations are roughly 2.1 and 9.4. Equilibrium studies of the alkaline pK reveal that more than one berne-linked proton is dissociated in this pH range. The carboxymethylated product of the cyanide complex of oxidized cytochrome ƒ has the same properties as cytochrome c carboxymethylated under the same conditions. The results suggest that a methionine sulfur is involved in iron coordination in oxidized Euglena cytochrome ƒ [ABSTRACT FROM AUTHOR]