On the compounds of ferricytochrome C appearing in acid solution

Abstract

1. 1. The absorption spectra in the Soret band region and the magnetic properties of ferricytochrome c at various chloride ion concentrations have been reinvestigated within the range pH 1–5. 2. 2. The form of ferricytochrome c, which exists at neutral pH (“Cyt”, β max = 23.3 · 10 7 cm 2 × mole −1 at 408 m μ) changes upon acidification to an acid form (“Cyt-2H+”, β max = 50 · 10 7 cm 2 × mole −1 at 395 m μ) with the simultaneous uptake of two protons ( n = 2). Half of the total spectral change is reached at pH 2.12. Simultaneously to the spectral change the paramagnetic susceptibility increases from χ m = 2120 (1 odd electron) to 16, 200 · 10 −6 cgs emu (5 odd electrons). The values for Cyt-2H + have been obtained by extrapolation to [Cl −] = 0. 3. 3. When increasing amounts of chloride ions are added to a solution, containing cytochrome c mainly as Cyt-2H +, the cytochrome is gradually converted into another form, denoted Cyt-2H +-sCl − ( β max = 25.8 · 10 7 cm 2 × mole −1 at 402 m μ). Two chloride ions are taken up simultaneously n = 2. K Cl − was found to be 7.10 −3 M 2 at pH 1 and about ten times lower at pH 2 and 3. Parallelling these spectral changes the paramagnetic susceptibility decreases to χ m =6000 at pH 3 and 7400 · 10 −6 cgs emu at pH 1.5 (3 odd electrons). The differences in K Cl − and χ m of Cyt-2H +-2Cl − at pH 1–1.5 are tentatively explained as depending upon protein disconfiguration due to the acid milieu. 4. 4. The change from Cyt to Cyt-2H + is interpreted as corresponding to a replacement of covalent links between the iron atom and the two hemichrome-forming groups of the protein moiety by ionic links. In Cyt-2H +-2Cl − a dipole chain arrangement is assumed.