Nitrite reduction by CoII and MnII substituted myoglobins: Towards understanding necessary components of Mb nitrite reductase activity

摘要: Abstract Nitrite reduction to nitric oxide by heme proteins is drawing increasing attention as a protective mechanism hypoxic injury in mammalian physiology. Here we probe the nitrite reductase (NiR) activities of manganese(II)- and cobalt(II)-substituted myoglobins, compare with data obtained previously for iron(II) analog wt Mb II . Both Mn Co displayed NiR activity, it was shown that kinetics are first order each [protein], [nitrite], [H + ], determined Fe The second rate constants ( k 2 ) at pH 7.4 T  = 25 °C, were 0.0066 0.015 M − 1  s Mb, respectively, both orders magnitude slower than (6 M final reaction products consisted mixture nitrosyl Mb(NO) III similar from analogous Mb. In contrast, found be nitrito complex Mb(ONO − plus roughly an equivalent free NO. differences can attributed part stronger coordination inorganic reflected respective M formation K : 2100 M (Co (Mn ). We also report (3.7 30 M , respectively) complexes mutant metmyoglobins H64V (NO H64V/V67R (ONO revised value (120 M metMb. values three ferric emphasize importance H-bonding residue, such His64 distal pocket or Arg67 stabilizing coordination. Notably, corresponding ferrous Mbs follow sequence suggesting binding these centers analogously affected residues.