Nonheme iron enzyme

Huynh BH, Czechowski MH, Kruger HJ, et al. 1984. Desulfovibrio vulgaris hydro-genase a nonheme iron enzyme lacking nickel that exhibits anomalous EPR and Mossbauer spectra. Proc Natl Acad Sci USA 81 3728-32. 

The nonheme iron enzymes discussed so far in this section either utilize oxygen as a substrate or form it as a product. Other nonheme iron sites that do not bind O2 as part of their catalytic function have similar ligand environments. An example of such a system is the QFe site associated with the reaction centers of photosynthetic bacteria and with photosystem II of chloroplasts (Feher et al., 1989). 

The P. chlororaphis B23 NHase is the ferric enzyme [50], which has been characterized in detail [51,52]. (i) The NHase is the first known nonheme iron enzyme containing a typical low-spin Fe(III) site, (ii) the axial position of the Fe(III) site in the enzyme may be occupied by aquo and sulfhydryl groups, and (iii) aliphatic nitrile substrates directly bind to the Fe(III)-active center through H20-substrate replacement. The NHase also seems to contain pyrroloquinoline quinone (PQQ) or a PQQ-like compound [53]. 

Because of the increasing availability of protein structures, our understanding of nonheme iron enzymes with mononuclear active sites has also developed significantly since the first edition of this book. In addition to the previously reported... 

There has been much progress in recent years in our understanding of nonheme iron enzymes that activate dioxygen, particularly with respect to structure. From this vantage point, I have attempted to assemble the mechanistic ideas for these enzymes, using experimental evidence whenever available to support the proposed mechanisms. These mechanisms will evolve and need refinement as new data are reported. The various mechanisms discussed here appear to have a com-... 

Activity in the area of nonheme iron enzymes continues to flourish, with several exciting results being published in this subfield since Chapter 10 was submitted. 

In the area of mononuclear nonheme iron enzymes, x-ray crystal structures are now also available for the catalytic domain of human phenylalanine hydroxylase [18] and naphthalene 1,2-dioxygenase [19]. The mononuclear iron site of phenylalanine hydroxylase resembles the 2-His-l-Asp site of tyrosine hydroxylase, a result anticipated by sequence homology. More interestingly, naphthalene 1,2-dioxygenase, which catalyzes the c/ s-dihydroxylation of arene double bonds in the biodegradation of aromatics, also has a Fe(His)2(Asp) iron site. These two enzymes augment the increasing number of mononuclear nonheme iron enzymes with a common Fe(His)2(carboxylate) facial triad motif [20],... 

Solomon El, Wong SD, Liu LV, Decker A, Chow MS. Peroxo and oxo intermediates in mononuclear nonheme iron enzymes and related active sites. Curr Opin Chem Biol. 2009 13 99-113. 

IsopeniciUin N synthase (IPNS) is a nonheme iron enzyme found in Cephalosporium, Penicillium, and Streptomyces strains. It activates O2 and catalyzes the formation of isopeniciUin N from 5-(L-Q -amtnoadipoyl)-L-cysteinyl-D-valine (ACV) (Figure 13). Interestingly, it has the conserved HX(D/E)XmHX RXS sequence motif, similar to those found in many 2-oxoglutarate-dependent enzymes but does not require 2-oxoglutarate for activity. ... 

The above description is of standard TRIPLE, i.e., exphcit TRIPLE, employing two rf energies. Pnlsed ENDOR can also exhibit relative sign information, in the absence of an additional rf energy. This phenomenon has been called implicit TRIPLE , and was demonstrated for nitrile hydratase, a nonheme iron enzyme (low-spin Fe , S = 1/2). Standard Mims ENDOR experiments were performed and the intensities of signals for H were compared for natural... 

Lange, S. J., Que, L., Jr. (1998). Oxygen activating nonheme iron enzymes. Current Opinion in Chemical Biology, 2, 159—172. 

Catechol dioxygenases are nonheme iron enzymes which catalyze the oxidative cleavage of catechols. [Fe(Cat)(Tp )(Hpz )] [Cat = catecholate = C6H4O2, 3,5- Bu2, C6H2O2, C6CI4O2) have been prepared and their reactivity toward O2 investigated.94... 

High-valent iron intermediates have been proposed as the active species in OAT and C-H oxidation reactions for nonheme iron enzymes. In some cases, such intermediates have been trapped by rapid fireeze-quench studies and characterized. In ribonucleotide reductase from E. coli and MMO, intermediates X and Q with Fem-( l-0)2-Ferv and Ferv-( 0,-O)2-FeIV diamond core, respectively, have been characterized (Figure 3.11).35 Also, Fe,v oxo intermediates have been observed for mononuclear proteins such as taurine/2-oxoglutarate dioxygenase (TauD) (Figure 3.11).36... 

FIGURE 3.10 Representative reactions of nonheme iron enzymes. 

Shearer, J., R.C. Scarrow, and J.A. Kovacs (2002). Synthetic models for the cysteinate-ligated nonheme iron enzyme superoxide reductase Observation and structural characterization by XAS of an Fe(IIl)-OOH intermediate. J. Am. Chem. Soc. 117, 11709-11717. 

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