1H, 13C, and 15N backbone, side-chain, and heme chemical shift assignments for oxidized and reduced forms of the monoheme c-type cytochrome ApcA isolated from the acidophilic metal-reducing bacterium Acidiphilium cryptum.

We report the (1)H, (13)C, and (15)N chemical shift assignments of both oxidized and reduced forms of an abundant periplasmic c-type cytochrome, designated ApcA, isolated from the acidophilic gram-negative facultatively anaerobic metal-reducing alphaproteobacterium Acidiphilium cryptum. These resonance assignments prove that ApcA is a monoheme cytochrome c (2) and the product of the Acry_2099 gene. An absence of resonance peaks in the NMR spectra for the 21N-terminal residues suggests that a predicted N-terminal signal sequence is cleaved. We also describe the preparation and purification of the protein in labeled form from laboratory cultures of A. cryptum growing on (13)C- and (15)N- labeled substrates.