Conserved Met16 of Pseudoazurin Facilitates the Interprotein Electron Transfer to Copper-Containing Nitrite Reductase

Enzyme reaction of copper-containing nitrite reductase relies on the electron donor, pseudoazurin, yet the role of conserved pseudoazurin Met16 in electron transfer remains unclear. Combining cyclic voltammetry and stopped-flow kinetics, we show Met16 variants reduce kapp to 10–31 % of wild type and lower kcat/Km to 20–27%, indicating impaired complex formation and catalytic efficiency.