The Met80Ala variant of yeast iso-1-cytochrome c, immobilized on a gold electrode, is found to exchange electrons efficiently with it in nondenaturing conditions and to provide robust and persistent catalytic currents for O-2 and nitrite ion reduction from pH 3 to 11. Direct covalent protein linkage to gold yields the best electrochemical and electrocatalytic performances without drastically affecting the structural properties of the bound protein compared to the freely diffusing species. Therefore, this biocatalytic interface can be of use for the amperometric detection of the above species, which are of great environmental, industrial, and clinical interest, with particular reference to the exploitation in nanostructured biosensing devices. This work shows that the use of a small engineered electron transfer (ET) protein, featuring an axial heme iron coordination position available for the binding of exogenous ligands, in place of a large heme enzyme is a viable strategy for the improvement of the heterogeneous ET rate and the stability and efficiency of sensing gold-protein interfaces over a wide range of T and pH.