FIG. 2.

SenX3 is oxidized by O₂. (A) SenX3 protein was exposed to air for 2 min after DTH treatment. The air-exposed SenX3 was then treated with a 100-fold molar excess of KCN, which produced a peak at 540 nm, indicating the presence of a met-CN⁻ complex. Insets display enlarged images of the 500–600 nm regions. (B) DTH-treated SenX3 does not react with KCN. Exposure of DTH-treated SenX3 to a 100-fold molar excess of KCN does not result in any spectral changes, but it only reacts with KCN after treatment with a 500-fold molar excess of the chemical oxidant Fe(CN)₆³⁻ (C). (D) Air-exposed SenX3 does not react with CO. Air-exposed SenX3 was treated with a 100-fold molar excess of CO donor CORM-2. It is very well known that CO does not react with met-heme proteins. In agreement with this, we did not observe any spectral changes in the air-exposed SenX3 on CO treatment. Numbers in parentheses denote absorption maximum in nanometers. KCN, potassium cyanide. To see this illustration in color, the reader is referred to the web version of this article at www.liebertpub.com/ars