On the Origin of the Low-Spin Character of Cytochrome P450cam in the Resting State—Investigations of Enzyme Models with Pulse EPR and ENDOR Spectroscopy

Abstract

The P450 enzyme model 1 is a high-spin system. EPR and ENDOR spectra reveal the coordination of water to the Fe center. This is the first experimental proof that coordination of water is not the single determining factor in the stabilization of the low-spin character of the cytochrome P450 resting state.

Studying high-spin ferric heme proteins by pulsed EPR spectroscopy: Analysis of the ferric form of the E7Q mutant of human neuroglobin

“…3a). The observed proton splitting is similar to the one found for the protons of axially bound water in a HS ferric porphyrin system [5], confirrning the peak assignment to the water ligand protons of aquometmyoglobin.…”

“…1 Introduction 24 years after the seminal continuous-wave (CW) electron-nuclear double resonance (ENDOR) study of single crystals of aquometmyoglobin by Charles Scholes, in which also George Feher was involved [1], the number of ENDOR and pulsed electron paramagnetic resonance (EPR) studies on high-spin fer¡ heme proteins is still very low [2][3][4][5]. This is in strong contrast to the rapid methodological and instrumental developments in the fietd of EPR of the last two decennia [6].…”

A Versatile and Convenient Method for the Functionalization of Porphyrins

“…The significant ∆δ ϭ Ϫ1.3 for H 2 Ј may appear to be inconsistent with the negligible ∆δ value of the benzylic methylene group. However, in the free base, if we consider that the two aromatic rings of the picket, conjugated through the amide bond, are not coplanar ( Figure 1) as generally reported, [24,25] the aromatic cycle of the picket is not perpendicular to the porphyrin plane but somehow in a flattened position and offset from the centre of the porphyrin. The coordination of the nitrogen base should therefore induce the movement of this aromatic ring in a perpendicular position as the 2-MeIm is directly attached to the benzyl group.…”

“…This type of spatial control has already been described for porphyrins with pickets built with Kemp's triacid. [24,25] Unfortunately, the reaction conditions to achieve this coupling cannot be applied to either isomer of TAPP because of its possible atropisomerization. On the other hand, 3-(chloromethyl)benzoic acid, owing to its meta benzyl linkage, has been shown to enforce the coordination of an imidazole to a heme.…”

Unravelling novel synergies between organometallic and biological partners: a quantum mechanics/molecular mechanics study of an artificial metalloenzyme

“…catalase [20]) or an octahedral low-spin configuration (i.e. peroxidases [21], cytochromes P450 [22] or haem oxygenase [23]) with only one residue of their apo-protein bound to the metal in the axial position and, eventually, one labile water molecule coordinated on the distal site of the haem to complete the octahedral configuration of the metal (figure 1). The strength of the coordination of this water molecule can be influenced by its environment and, in turn, conditions the transition from hexacoordinated resting states to active pentacoordinated species [24].…”