Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.7.1.4 (nitrite reductase)
 1,847 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

c-type cytochromes are characterized by covalent attachment of haem to the protein by two thioether bonds formed between the haem vinyl groups and the cysteine sulphurs in a CXXCH peptide motif. In Escherichia coli and many other Gram-negative bacteria, this post-translational haem attachment is catalysed by the Ccm (cytochrome c maturation) system. The features of the apocytochrome substrate required and recognized by the Ccm apparatus are uncertain. In the present study, we report investigations of maturation of cytochrome b562 variants containing CXXCR, CXXCK or CXXCM haem-binding motifs. None of them showed any evidence for correct maturation by the Ccm system. However, we have determined, for each variant, that the proteins (i) were expressed in large amounts, (ii) could bind haem in vivo and/or in vitro and (iii) were not degraded in the cell. Together with previous observations, these results strongly suggest that the apocytochrome substrate feature recognized by the Ccm system is simply the two cysteine residues and the histidine of the CXXCH haem-binding motif. Using the same experimental approach, we have also investigated a cytochrome b562 variant containing the special CWSCK motif that binds the active-site haem of E. coli nitrite reductase NrfA. Whereas a CWSCH analogue was matured by the Ccm apparatus in large amounts, the CWSCK form was not detectably matured either by the Ccm system or by the dedicated Nrf biogenesis proteins, implying that the substrate recognition features for haem attachment in NrfA may be more extensive than the CWSCK motif.
 ...
PMID:The histidine of the c-type cytochrome CXXCH haem-binding motif is essential for haem attachment by the Escherichia coli cytochrome c maturation (Ccm) apparatus. 1580 11

Globins, such as hemoglobin (Hb) and myoglobin (Mb), have gained attention for their ability to reduce nitrite (NO2(-)) to nitric oxide (NO). The molecular interactions that regulate this chemistry are not fully elucidated, therefore we address this issue by investigating one part of the active site that may control this reaction. Here, the effects of the 2,4-heme substituents on the nitrite reductase (NiR) reaction, and on the structures and energies of the ferrous nitrite intermediates, are investigated using Mb as a model system. This is accomplished by studying Mbs with hemes that have different 2,4-R groups, namely diacetyldeuteroMb (-acetyl), protoMb (wild-type (wt) Mb, -vinyl), deuteroMb (-H), and mesoMb (-ethyl). While trends on the natural charge on Fe and O-atom of bound nitrite are observed among the series of Mbs, the Fe(II)-NPyr (Pyr=pyrrole) and Fe(II)-NHis93 (His=histidine) bond lengths do not significantly change. Kinetic analysis shows increasing NiR activity as follows: diacetyldeuteroMb<wt Mb<deuteroMb<mesoMb. Nitrite binding energy calculations of the different Mb(II)-nitrite conformations demonstrate the N-bound complexes to be more stable than the O-bound complexes for all the different types of heme structures, with diacetyldeuteroMb having the greatest nitrite binding affinity. Spectral deconvolution on the final product generated from the reaction between Mb(II) and NO2(-) for the reconstituted Mbs indicates the formation of 1:1 Mb(III) and Mb(II)-NO. The electronic changes induced by the -R groups on the 2,4-positions do not alter the stoichiometric ratio of the products, resembling wt Mb.
...
PMID:Modulating the nitrite reductase activity of globins by varying the heme substituents: Utilizing myoglobin as a model system. 2654 4