FIG. 9.

Model of hmp and nasDEF regulation in response to nitrosative stress. During nitrosative stress inflicted by SNP, nitrosylation of NsrR results in derepression of hmp and nasDEF (consistent with the model previously suggested by Nakano et al. [24]). Under oxic conditions Hmp detoxifies NO to NO₃⁻. However, when Hmp is present in the absence of NO, superoxide that inactivates the enzyme is produced. ResD, presumably in its phosphorylated form, is required for expression of nasDEF and enhances transcription from the hmp promoter (indicated by the dashed arrow). The mechanism of activation of ResD by SNP is not known (indicated by the gray arrows).