Protoheme, chelated

Since C has been assigned to a triplet deoxy state in which the axial ligand has been dissociated. As can be seen in Table 111, in most cases lifetimes are found to compare favorably between the carbon monoxide and oxygen forms of the synthetic complexes. In all cases the rate constants used had an accuracy of only one significant figure, resulting in an accuracy no better for the lifetimes or these states. One noticeable discrepancy in occurs between the chelated protoheme 1 -CO and the oxygen form of this compound, i 02. 

R = ethyl chelated mesoheme R = vinyl chelated protoheme... 

Table II. Comparison of Spectroscopic and Kinetic Properties of Hemoglobin and Chelated Protoheme ...

Extinction coefficients, mM, in parentheses data for Hb from Ref. 1 for chelated protoheme from Ref. 26 and 30. c See Table I for hemoglobin references the oxygen rates are the average of the a and j3 chains. The chelated protoheme rates are from Ref. 26 and 30. 

Ferrochelatase (protoheme ferro-lyase)401 403 inserts Fe2+ into protoporphyrin IX to form heme. The enzyme is found firmly bound to the inner membrane of mitochondria of animal cells, chloroplasts of plants, and chromatophores of bacteria. While Fe2+ is apparently the only metallic ion ordinarily inserted into a porphyrin, the Zn2+ protoporphyrin chelate accumulates in substantial amounts in yeast, and Cu2+-heme complexes are known (p. 843). Ferrochelatase, whose activity is stimulated by Ca2+, appears to be inhibited by lead ions, a fact that may account for some of the acute toxicity of lead.404... 

Biosynthesis synthesis The biosynthesis from protoporphyrin proceeds through chelatization of an iron(ll) ion catalyzed by ferrochelatase (protoheme ferrolyase, EC 4.99.1.1). Tlie H. in red blood particles is degraded to bile pigments after an average life-time of ca. 120 d. 

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