Nitrite reductase: Difference between revisions

Protein film voltammetry (PFV) experiments performed on ''S. oneidensis'' ccNiR films in the absence of substrate produced a broad envelope of reversible signals that span approximately 450 mV. At high pH values the envelope appears as a single peak, whereas at pH values below 7 the envelope appears to be composed of two large overlapping peaks. At pH values below 6 and at 0 °C, the envelope of signal can be better resolved and more than two peaks can be observed. This resulting envelope of signal can be deconvoluted as the sum of five one-electron peaks, each corresponding to one of the five hemes in a ccNiR monomer (see image below).  

[[Image:figur5.jpg|left|378px|thumb|PFV of ''S. oneidensis'' ccNiR (a) Typical signal on a graphite electrode. (b) Baselinesubtracted non-turnover voltammogram]]   

The Ca²⁺ ion within <scene name='Journal:JBIC:16/Cv/14'>conserved site</scene> is coordinated in bidentate fashion by <scene name='Journal:JBIC:16/Cv/15'>Glu205</scene>, and in monodentate fashion by the <scene name='Journal:JBIC:16/Cv/16'>Tyr206 and Lys254</scene> backbone carbonyls, and the <scene name='Journal:JBIC:16/Cv/17'>Gln256</scene> side-chain carbonyl. In the ''S. oneidensis'' structure only <scene name='Journal:JBIC:16/Cv/18'>one water molecule</scene> is assigned to the Ca²⁺ ion in subunit B. In subunit A the difference electron density that represents this water molecule is very close to the noise level, and it is difficult to identify even one water molecule there. The <scene name='Journal:JBIC:16/Cv/14'>carbonyl side chain of Asp242 and the hydroxyl of Tyr235</scene> come near to the open calcium coordination sites, but are not within bonding distance. Instead they interact with the water molecule that is weakly coordinated to the Ca²⁺ ion. The ccNiR calcium ions appear to play a vital role in organizing the <scene name='Journal:JBIC:16/Cv/13'>active site</scene> (as was mentioned above <font color='magenta'><b>hemes-1</b></font> are the active sites).