INCORPORATION OF NORVALINE AT LEUCINE POSITIONS IN RECOMBINANT HUMAN HEMOGLOBIN EXPRESSED IN ESCHERICHIA-COLI

We report here a novel finding that norvaline can be incorporated in p lace of leucine in recombinant human hemoglobin expressed in Escherich ia coli, The presence of the norvaline was confirmed by several analyt ical methods such as amino acid analysis, peptide mapping, electrospra y mass spectrometry, and Edman protein sequencing, It appears that sub stitution is distributed across both the beta- and di-alpha-globins in purified recombinant hemoglobin, The level of misincorporation correl ated with the ratio of the free norvaline/leucine pool available in th e cell culture, This suggests that the incorporation of norvaline for leucine occurs through misaminoacylation of tRNA(Leu), similar to the misincorporation of norleucine for methionine found in many recombinan t proteins expressed in E. coli.