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J. Bacteriol. doi:10.1128/JB.01388-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Heme concentration dependence and metalloporphyrin inhibition of the system I and II cytochrome c assembly pathways

Washington University, Department of Biology Campus Box 1137, 1 Brookings Drive St. Louis, MO 63130; University of Rochester, Department of Pharmacology and Physiology, Box 711, 601 Elmwood Ave. Rochester, NY 14642

^* To whom correspondence should be addressed. Email: kranz{at}biology.wustl.edu.

	Abstract

Studies have indicated that specific heme delivery to the apocytochrome c is a critical feature of the cytochrome c biogenesis pathways called system I and II. To determine directly the heme requirements of each system, including if other metal porphyrins can be incorporated into cytochromes c, we engineered Escherichia coli such that the natural system I (ccmABCDEFGH) is deleted and exogenous porphyrins are the sole source of porphyrins (hemA). These engineered E. coli that produce recombinant system I (from E. coli) or system II (from Helicobacter) facilitated studies on the heme concentration dependence of each system. Using this exogenous porphyrin approach it is shown that system I uses heme at least 5 fold lower levels than system II, addressing an important advantage for system I. Neither system could assemble holocytochromes c with other metal porphyrins, suggesting that the attachment mechanism is specific for Fe protoporphyrin. Surprisingly, Zn and Sn protoporphyrins are potent inhibitors of the pathways and exogenous heme competes with this inhibition. It is proposed that the targets are the heme binding proteins within the pathways (CcmC, CcmE, and CcmF for system I and CcsA for system II).

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