Figure 6. Spectral intermediates in the OleT catalytic cycle.

From top left to bottom left in a clockwise direction, the UV–visible spectra for four key P450 catalytic cycle species are shown. Top left: the ferric, high-spin form of OleT, as observed for the OleT complex with arachidic acid (C20:0). The Soret peak is at 396 nm, with a small feature at 650 nm indicative of a cysteine thiolate-to-high-spin ferric heme iron charge-transfer species. Top right: the spectrum of OleT compound I (Fe^IV=oxo porphyrin radical cation) with characteristic spectral maxima at ∼370 and 690 nm. Bottom right: the OleT compound II (Fe^IV-hydroxo) spectrum following hydrogen atom abstraction from the substrate and with a Soret peak maximum at 426 nm. Bottom left: the spectrum of the resting, low-spin ferric form of OleT following completion of the catalytic cycle and with the Soret maximum at 417 nm.