Ring Nonplanarity and Aromaticity in Porphyrins. Nuclear Magnetic Resonance Spectra of Etioporphyrin II and Its N-Alkyl Compounds

Caughey, Winslow S.; Iber, Peter K.

doi:10.1021/jo01036a538

Cited by 21 publications

(6 citation statements)

References 3 publications

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“…NMPP has long been known to be a potent inhibitor of mammalian ferrochelatase, which competes with the porphyrin substrate for binding to the enzyme [16,17]. Since alkylation of a pyrrole nitrogen atom introduces non-planarity into the porphyrin macrocycle [23], the inhibitory properties of NMPP are thought to arise from its structural resemblance to the distorted porphyrin intermediate in the ferrochelatase-catalysed reaction [2]. In addition, the analysis of the X-ray crystal structural of Bacillus subtilis ferrochelatase complexed with N-methylmesoporphyrin indicated that the active-site loop residues are in close proximity to the porphyrin macrocycle [7].…”

Section: Resultsmentioning

confidence: 99%

Modulation of inhibition of ferrochelatase by N-methylprotoporphyrin

Shi

Ferreira

2006

Biochemical Journal

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Protoporhyrin IX ferrochelatase catalyses the terminal step of the haem-biosynthetic pathway by inserting ferrous iron into protoporphyrin IX. NMPP (N-methylprotoporphyrin), a transition-state analogue and potent inhibitor of ferrochelatase, is commonly used to induce haem deficiency in mammalian cell cultures. To create ferrochelatase variants with different extents of tolerance towards NMPP and to understand further the mechanism of ferrochelatase inhibition by NMPP, we isolated variants with increased NMPP resistance, bearing mutations in an active-site loop (murine ferrochelatase residues 248-257), which was previously shown to mediate a protein conformational change triggered by porphyrin binding. The kinetic mechanisms of inhibition of two variants, in which Pro255 was replaced with either arginine (P255R) or glycine (P255G), were investigated and compared with that of wild-type ferrochelatase. While the binding affinity of the P255X variants for NMPP decreased by one order of magnitude in relation to that of wild-type enzyme, the inhibition constant increased by approximately two orders of magnitude (K(i)(app) values of 1 microM and 2.3 microM for P255R and P255G respectively, as against 3 nM for wild-type ferrochelatase). Nonetheless, the drastically reduced inhibition of the variants by NMPP was not paralleled with a decrease in specificity constant (kcat/K(m, protoporhyrin IX)) and/or catalytic activity (kcat). Further, although NMPP binding to either wild-type ferrochelatase or P255R occurred via a similar two-step kinetic mechanism, the forward and reverse rate constants associated with the second and rate-limiting step were comparable for the two enzymes. Collectively, these results suggest that Pro255 has a crucial role in maintaining an appropriate protein conformation and modulating the selectivity and/or regiospecificity of ferrochelatase.

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Section: Resultsmentioning

confidence: 99%

Modulation of inhibition of ferrochelatase by N-methylprotoporphyrin

Shi

Ferreira

2006

Biochemical Journal

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“…The central N-substituent cannot fit into the inner cavity of the porphyrin macrocycle and consequently causes a distortion of the N-alkylated ring which is significantly tilted out of the porphyrin plane; this is particularly so in the Results given were obtained with the same preparation of mouse liver mitochondria (as the source of ferrochelatase) employing/>3 different concentrations of inhibitor [5 ]. The pure isomers, obtained from unresolved synthetic N-methyl protoporhyrin as in [ 3 ], were only tested once; all other results were confirmed in ~>2 additional experiments metal chelate derivatives where the space available in the centre of the porphyrin system is further reduced by the presence of a metal [13][14][15][16]. We therefore suggest that when a propionlc acid-substituted ring is N-methylated, the alignment of the 2 propionic acid chains with respect to each other may be significantly altered ( fig.l, cf.…”

Section: Differential Inhibition Of Ferrochelatase By Different Strucmentioning

confidence: 97%

Structural Isomerism and chirality of N‐monosubstituted protoporphyrins

Matteis

Jackson²,

Gibbs

et al. 1982

FEBS Letters

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“…If the methylation was carried out with methyl iodide in a sealed tube at IOO'C, an N,N',N"-trimethyl derivative was formed, (15 ? ), analogous to the N,N',N"-trimethylporphyrin, and (17) and (18) were also prepared.6 Methylation of a copper corrole anion was originally thought to occur on the metal, but x-ray analysis later showed that the product was the N-methyl copper corrole (19). 16 The N-alkyl corroles formed stable copper and palladium complexes, but the zinc complexes were unstable and did not form nickel complexes.…”

Section: Et E Lmentioning

confidence: 99%