Heme proximal ligand

Fig. 3. Push-pull mechanism for the heterolysis of the 0-0 bond of an iron-peroxo complex. The oval indicates an electron-rich ligand, such as a porphyrin L is a heme-proximal ligand (cysteine or histidine).

Evaluation of the contribution made by the proximal ligand to the oxidation-reduction equilibrium of Mb (H93 in the wild-type protein (Fig. 2)) has been more difficult because substitution of the proximal residue results in expression of apo-Mb without heme incorporation. All of the available data for these variants (Table I), therefore, derive from proteins prepared by reconstitution of purified recombinant apoprotein with exogenous heme 69, 70, 72). In those cases where trace quantities of native Mb are produced (73), heme extraction followed by reconstitution was undertaken to eliminate complications from suIfMb... 

Mutation of His 132 to an alanine, glycine, or serine in the truncated human heme oxygenase, in accord with identification of His25 as the proximal ligand, does not alter the cpe-His band in the resonance Raman spectrum of the Fe deoxy protein (82). The mutations result in the formation of two separate fractions when the protein is expressed in... 

Roach MP, Chen YP, Woodin SA, Lincoln DE, Lovell CR, Dawson JH (1997) Notomastus lobatus Chloroperoxidase and Amphitrite ornata Dehaloperoxidase Both Contain Histidine as Their Proximal Heme Iron Ligand. Biochemistry 36 2197... 

Franzen S, Roach MP, Chen Y-P, Dyer RB, Woodruff WH, Dawson JH (1998) The Unusual Reactivities of Amphitrite ornata Dehaloperoxidase and Notomastus lobatus Chloroperoxidase Do Not Arise from a Histidine Imidazolate Proximal Heme Iron Ligand. J Am Chem Soc 120 4658... 

Yi X, Mroczko M, Manoj KM, Wang X, Hager LP (1999) Replacement of the Proximal Heme Thiolate Ligand in Chloroperoxidase with a Histidine Residue. Proc Natl Acad Sci U S A 96 12412... 

Poulos TL (1996) The role of the proximal ligand in heme enzymes. J Biol Inorg Chem 1 356-359... 

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