The area of hemoprotein research has advanced dramatically in recent years with the advent of molecular cloning techniques. The availability of high level expression systems for hemoproteins, such as the cytochrome P-450 enzymes, and the ability to generate site-directed mutants has advanced our knowledge of both mechanism and structure. The rapidly expanding role of hemoproteins in cell signaling processes typified by the eukaryotic nitric oxide synthases and soluble guanylate cyclase, and in gene regulation with transcription factors such as CooA, has expanded the repertoire of hemoprotein motifs. It

Figure 5. Resonance Raman spectra of the ferrous heme:HO-1 complex and the manganese (II) protoporphyrin:HO-1 complex in the low frequency region (441.6 nm excitation). The resonance Raman data for the heme:HO-1 complex has previously been reported (111).

is with great anticipation that we look forward to the discovery of new and unique hemoproteins and the critical role they may play in molecular and cellular processes.

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