General Background : Hemes Heme (protoheme, heme b) is an iron-containing prosthetic group found in many essential proteins including cytochromes and heme-containing globins. In addition to its role in oxidative metabolism, heme also functions as a regulatory molecule in transcription, translation, protein targeting, protein stability, and cellular differentiation. Heme is a porphyrin member of the cyclic tetrapyrroles. Even though it is biosynthesized as : PROTOHEME, different derivatives of protoheme can be formed that differ in modifications to the porphyrin ring, including how it is bound to the protein, such as : HEME_O, : HEME_A, : HEME_C, and : HEME_D. This pathway describes the aerobic route for : PROTOHEME biosynthesis. This pathway involves the enzymes : COPROGENOXI-MONOMER and : MONOMER-17460, which require moelecular oxygen for their respective reactions. There are several types of protoporphyrinogen oxidases: in most eukaryotes and many aerobic or facultative bacteria, such as Firmicutes, the enzyme is a FAD-dependent ~55 kDa protein encoded by the : BSU10140 gene. A number of gamma-proteobacteria, including Escherichia coli, have another type of oxidase, a 21 kDa protein encoded by the : EG11485 gene. Most archaea and many other bacteria, including the majority of cyanobacteria, have a third version of the enzyme, a 24 kDa protein encoded by : G-15222

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