Resonance Raman spectroscopy of oxoiron(IV) porphyrin π-cation radical and oxoiron(IV) hemes in peroxidase intermediates

Terner, James; Palaniappan, Vaithianathan; Gold, Avram; Weiss, Raymond; Fitzgerald, Melissa M.; Sullivan, Ann; Hosten, Charles M.

doi:10.1016/j.jinorgbio.2006.01.008

Cited by 80 publications

(82 citation statements)

References 270 publications

(526 reference statements)

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“…Although the observation of this single feature, appearing at 791 cm −1 , is obviously consistent with an intermediate with "peroxo-like" character, it must be noted that this vibrational frequency and 16 O/ 18 O isotopic shifts are close to what is expected for the ν(Fe = O) mode of a ferryl heme species; the frequencies of such ferryl species depend on the transaxial ligand and distal pocket interactions, with reported values ranging from 745 cm −1 up to about 800 cm −1 (34,36). However, the assignment of this feature to a ferryl species was ruled out by experiments conducted with scrambled oxygen, a (1:2:1) mixture of 16 Fig.…”

Section: Resultssupporting

confidence: 79%

Unveiling the crucial intermediates in androgen production

Mak

Gregory

Denisov

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

189

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Ablation of androgen production through surgery is one strategy against prostate cancer, with the current focus placed on pharmaceutical intervention to restrict androgen synthesis selectively, an endeavor that could benefit from the enhanced understanding of enzymatic mechanisms that derives from characterization of key reaction intermediates. The multifunctional cytochrome P450 17A1 (CYP17A1) first catalyzes the typical hydroxylation of its primary substrate, pregnenolone (PREG) and then also orchestrates a remarkable C 17 -C 20 bond cleavage (lyase) reaction, converting the 17-hydroxypregnenolone initial product to dehydroepiandrosterone, a process representing the first committed step in the biosynthesis of androgens. Now, we report the capture and structural characterization of intermediates produced during this lyase step: an initial peroxo-anion intermediate, poised for nucleophilic attack on the C 20 position by a substrate-associated H-bond, and the crucial ferric peroxo-hemiacetal intermediate that precedes carbon-carbon (C-C) bond cleavage. These studies provide a rare glimpse at the actual structural determinants of a chemical transformation that carries profound physiological consequences.T he excessive production of androgen, which effectively fuels the progression of cancer, especially prostate cancer, was first treated by surgical methods (1), whereas more modern approaches are focused on the discovery and development of pharmaceuticals that can selectively inhibit androgen synthesis (2, 3). A member of the cytochrome P450 superfamily (4, 5), cytochrome P450 17A1 (CYP17A1), occupies a central role in the biosynthesis of steroid hormones in humans. As was first reported by Nakajin and Hall (6) and Nakajin et al. (7) for CYP17 from pig testis, this enzyme catalyzes two fundamentally different types of chemical transformations (5-11), with the first being the efficient hydroxylation of both of its primary substrates, pregnenolone (PREG) and progesterone (PROG), to 17-hydroxypregnenolone (17-OH) PREG and 17-hydroxypregnenolone, respectively (Fig. 1). Importantly, 17-OH PREG is further processed in a second step in which CYP17A1 now catalyzes, not another hydroxylation reaction, but a complex 17,20 carbon-carbon (C-C) bond cleavage (lyase) reaction. This step converts 17-OH PREG to dehydroepiandrosterone (DHEA), a process that represents a critical branch point in human steroidogenesis by providing the essential precursor to androgens and various corticosteroids (5-9). Although a similar C-C bond cleavage of 17-OH PROG is also mediated by CYP17A1, it is of less importance in humans because its efficiency is only about 2% of the efficiency of the physiologically important lyase reaction involving 17-OH PREG (10). Recognizing the intensive efforts currently underway to design and test substances that selectively inhibit CYP17A1 (2, 3), there is a pressing need to enhance our understanding of the relevant reaction mechanisms, a task that typically entails identification of key reaction intermediates. Dir...

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Section: Resultssupporting

confidence: 79%

Unveiling the crucial intermediates in androgen production

Mak

Gregory

Denisov

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

189

View full text Add to dashboard Cite

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“…It is important to note that the compound-II type of ferryl derivatives in general exhibit electronic transition bands similar to that of superoxo-ferric complexes (see ref. 43 and references therein), accounting for the fact that no intermediate other than the ternary complex was apparent in the transient spectra shown in Fig. 1 A. Additional studies carried out at an earlier time point, 80 ms, show that only the Fe-O2 / O-O modes at 563/1,137 cm Ϫ1 of the ferric superoxo intermediate were observable (see spectrum ii in Fig.…”

Section: Resultsmentioning

confidence: 85%

Evidence for a ferryl intermediate in a heme-based dioxygenase

Lewis-Ballester

Batabyal

Egawa

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

120

217

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In contrast to the wide spectrum of cytochrome P450 monooxygenases, there are only 2 heme-based dioxygenases in humans: tryptophan dioxygenase (hTDO) and indoleamine 2,3-dioxygenase (hIDO). hTDO and hIDO catalyze the same oxidative ring cleavage reaction of L-tryptophan to N-formyl kynurenine, the initial and rate-limiting step of the kynurenine pathway. Despite immense interest, the mechanism by which the 2 enzymes execute the dioxygenase reaction remains elusive. Here, we report experimental evidence for a key ferryl intermediate of hIDO that supports a mechanism in which the 2 atoms of dioxygen are inserted into the substrate via a consecutive 2-step reaction. This finding introduces a paradigm shift in our understanding of the heme-based dioxygenase chemistry, which was previously believed to proceed via simultaneous incorporation of both atoms of dioxygen into the substrate. The ferryl intermediate is not observable during the hTDO reaction, highlighting the structural differences between the 2 dioxygenases, as well as the importance of stereoelectronic factors in modulating the reactions. indoleamine 2,3-dioxygenase ͉ reasonance Raman spectroscopy ͉ tryptophan dioxygenase

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“…They are indicative of hydroxide ligation. Previous examinations of enzymatic ferryl species have reported ironoxygen stretching frequencies ranging from 745 to 821 cm Ϫ1 (25). In some cases, small (Ϸ3 cm Ϫ1 on average) upshifts in these frequencies have been reported in D 2 O (25, 26).…”

Section: Resultsmentioning

confidence: 97%