Figure 5.

Effect of steroid hormones on the peroxidase activity of CcO. (A) Effect of estradiol. Peroxidation of o-dianisidine was monitored by increase of absorption at 432 nm vs. 580 nm as a reference. The basic reaction medium (pH 7.6) with 1 mM DM contained 0.2 mM o-dianisidine and 0.6 µM CcO. The reaction was initiated by addition of 4 mM H₂O₂. Trace 1 (red)—recording in the presence of 0.5 mM estradiol benzoate, trace 2 (black)—the control. The initial jump upon H₂O₂ addition corresponds to spectral response of heme a₃ in CcO. Inset: 0.5 mM estradiol in the presence of 1 mM DM does inhibit cytochrome oxidase activity of CcO (see Figure 1A for more details). (B) Effect of testosterone (Tst). The conditions are as in panel A except that concentration of DM in the buffer was 20 mM. Trace 1 (red)—recording in the presence of 4 mM testosterone, trace 2 (black)—the control, trace 3 (blue)—testosterone (4 mM) was added during the reaction time course (indicated by the arrow), which was followed by temporary increase of turbidity (the supposed trajectory until spectral registration became possible is shown by the dashed line). Inset: 4 mM testosterone in the presence of 20 mM DM does inhibit oxidase activity of CcO (see Figure 2A for other conditions).