The Met80Ala variant of yeast iso-1-cytochrome c, immobilized on a gold electrode, is found toexchange electrons efficiently with it in nondenaturing conditions and to provide robust and persistent catalyticcurrents for O2 and nitrite ion reduction from pH 3 to 11. Direct covalent protein linkage to gold yields thebest electrochemical and electrocatalytic performances without drastically affecting the structural propertiesof the bound protein compared to the freely diffusing species. Therefore, this biocatalytic interface can beof 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. Thiswork shows that the use of a small engineered electron transfer (ET) protein, featuring an axial heme ironcoordination position available for the binding of exogenous ligands, in place of a large heme enzyme isa viable strategy for the improvement of the heterogeneous ET rate and the stability and efficiency ofsensing gold-protein interfaces over a wide range of T and pH.