Heme speciation in alkaline ferric FixL and possible tyrosine involvement in the signal transduction pathway for regulation of nitrogen fixation

Research was conducted to examine the heme speciation in alkaline ferric FixL and possible tyrosine involvement in the signal transduction pathway for regulation of nitrogen fixation. UV-visible, resonance Raman and electron paramagnetic resonance spectroscopy were used to measure the pH-dependent nature of the ferric forms of two soluble truncations of Rhizobium meliloti, designated FixL, FixL* and FixLN. Results indicate that the loss of activity at elevated pH cannot be attributed exclusively to the generation of a low-spin heme hydroxide.