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We have previously shown that human interferon α-2b (IFN) produced in Escherichia coli (E. coli) is heterogeneous at the N-terminal, with three major species (Ahsan et al., 2014). These are: (a) the direct translation product of the gene retaining the N-terminal methionine, (b) a species from which the methionyl residue has been removed by E. coli methionyl aminopeptidase to give the native interferon α-2b and (c) in which the N-terminal Cys residue of the latter contains an acetyl group. In this paper we overcome this heterogeneity, using engineered interferon derivatives with phenylalanine residue directly downstream of the N-terminal methionine (Met-Phe-IFN). This modification not only prevented the removal of the N-terminal methionine by E. coli methionyl aminopeptidase but also the subsequent N-acetylation. Critically, Met-Phe-IFN had enhanced activity in a biological assay. N-terminal stabilization was also achieved by fusing human cytochrome b 5 at the N-terminal of interferon (b 5 -IFN-chimera). In this case also, the protein was more active than a reciprocal chimera with cytochrome b 5 at the C-terminal of interferon (Met-IFN-b 5 -chimera). This latter protein also had a heterogeneous N-terminal but addition of phenylalanine following Met, (Met-Phe-IFN-b 5 -chimera), resolved this problem and gave enhanced biological activity., (Copyright © 2017 Elsevier Inc. All rights reserved.)