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The over expression and characterization of the three distinct heme-containing hydroperoxidases, katA, katB and katC from Sinohizobium meliloti is described. The results suggests that the combination of regulatory processes and of the kinetic parameters of the three hydroperoxidases appears to lead to an optimization of the S.meliloti capaity of H2O2 scavenging.

The dependence of autoxidation rate on oxygen concentration for Rhizobium meliloti FixL and Aplysia kurodai myoglobin with pentacoordinate met forms was determined. Results showed that the autoxidation mechanism used by the two proteins involved the reaction between a noncoordinated oxygen molecule and an intermediate with water coordinated to the ferrous heme iron. However, the absence of any link between the coordination of water and oxygen protection effect may also involved other mechanisms such as the transfer of electrons from oxyheme to deoxyheme.

The phosphotransfer between the purified CheA, CheY1 and CheY2 proteins and the spontaneous dephosphorylation rates of CheY1-P and CheY2-P were examined in vitro to describe the mechanism behind the reactions. The results support a four-step phosphotransfer including ATP-dependent autophosphorylation of CheA. CheY1 was found to act as a 'phosphatase' of CheY2-P by becoming a sink for phosphate in the presence of unphosphorylated CheA. It was also found to regulate the active, phosphorylated state of CheY2-P, the main response regulator.

The FixL spectra of Sinorhizobium meliloti by using Raman spectroscopy have shown dynamic structural changes due to ligand dissociation. The signal transduction of FixL is suggested to support the FG loop switch mechanism.

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.