The subunit structure of nitrite reductase purified from the denitrifier Achromobacter cycloclastes

The copper-containing nitrite reductase of Achromobacter cycloclastes has been considered to be a homotrimer with three identical subunits both in the crystal and in solution. In this study, however, the enzyme was found to be a heterotrimer consisting of two subunits with molecular masses of 37 kDa and 36.2 kDa, and the 37 kDa subunit was 6 amino acid residues longer than the smaller subunit. Signal-peptide cleavage sites in its N-terminal region are discussed.