\(Escherichia\) \(coli\) encounters nitrosative stress from various sources. It was shown in a previous study that a possible role for Hcp in the nitrosative stress response. The focus of this study was to determine the function of Hcp. The growth of the \(hcp\) mutant lacking all known NO reductases was inhibited by various sources of nitrosative stres. The growth defect was complemented by native Hcp protein, but not by mutated Hcp protein with a disrupted hybrid cluster. The role of Hcp was shown to protect \(E\). \(coli\) from nitrosative stress, and the hybrid cluster is critical for its function. Direct interaction between Hcp and its oxidoreductase Hcr was demonstrated. The \(hcp\)\(^+\)\(hcr\) strain showed that it was still resistant to nitrosative stress. Possibly alternative oxidoreductase of Hcp exists in \(E\). \(coli\). Gas analysis of the headspace of the anaerobic cultures showed that when treated with NO, the Hcp\(^+\) strain lacking all known NO reductases was still capable of reducing sub-micro molar NO into N\(_2\)O, while the further deletion of Hcp completely abolished NO reduction. This provides the first in vivo evidence that Hcp is a high affinity, low capacity NO reductase in \(E\). \(coli\).