Figure 2.

Absorbance changes of oxidized cytochrome bo₃ induced by (NH₄)₂SO₄. (A) Double difference absorption spectra of the isolated cytochrome bo₃ (4.8 μM): each spectrum is a difference between two difference spectra, (NH₄)₂SO₄-treated oxidized minus oxidized and K₂SO₄-treated oxidized minus oxidized at the same concentration of the sulfate. The arrows depict the direction of absorbance changes at increasing [(NH₄)₂SO₄]. (B) Absorbance changes measured at 416–400 nm as a function of [(NH₄)₂SO₄]. Experimental data (filled circles) are shown together with their best fit (solid line) to the hyperbolic equation (see Materials and Methods), giving the value for maximum absorption change at 416–400 nm A_max of 22.1 ± 0.6 mM⁻¹cm⁻¹, and K_dapp of 24.3 ± 2.7 mM (NH₄)₂SO₄ (4.9 ± 0.5 mM NH₃) (mean ± standard deviation, n = 3, R² = 0.98947).