Isobacteriochlorin cofactor

A protein may have more than one metal center, each with its own set of electronic transitions, and in favorable cases the RR spectra can be elicited selectively by judicious choice of laser wavelengths. For example, sulfite reductase has an iron-isobacteriochlorin cofactor, siroheme, which is coupled magnetically to a Fe4S4 cluster, probably through a thiolate bridge. The siroheme modes are strongly enhanced in resonance with the isobacteriochlorin Soret or Q bands, but intermediate excitation (457.9-488.0 nm) enhances the Fe4 4 cluster modes (Fig. 11). The protein rubrerythrin has two rubredoxin-like Fe(Cys)4 centers and a (/u.-oxo)di-iron(III) center (similar to those found in hemerythrins and ribonucleotide reductase), each of which can be enhanced selectively by excitation at... 

The siroheme aNiR, a crucial component of plant metabolism, contains an isobacteriochlorin cofactor - - , Scheme 4.3, which is tightly coupled to a... 

Heme d,6 another isobacteriochlorin, occurs as one of two cofactors in the reductase cytochrome cdj which mediates the nitrite reduction to nitrogen monoxide (NO) and from there to dinitrogen oxide (N20) in denitrifying bacteria.7... 

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