Primary sequence of a dimeric bacterial haemoglobin from Vitreoscilla

Vitreoscilla, a filamentous bacterium in the Beggiatoa family, synthesizes a soluble haemprotein which has two identical subunits of relative molecular mass 15,775 and two b haems per molecule1. It is synthesized in relatively large quantities when the organism, a strict aerobe, is grown under hypoxic conditions2. It forms a relatively stable oxygenated form which is spectrally similar to oxymyoglobin (oxyHb) and oxyhaemoglobin (oxyHb)3. The amino acid sequence of this protein has been determined and aligned to fit the helical regions of several animal and plant globins. This alignment is consistent with its being a structural homologue of the eucaryotic haemoglobins although it diverged from the others in the N-terminal region and may lack an A-helix. It showed the maximum sequence homology (24%) with lupin leghaemoblobin (Lb).Vitreoscilla Hb is the first bacterial haemoglobin to be sequenced. It may function to enable the organism to survive in oxygen-limited environments by acting as an oxygen storage-trap or to facilitate oxygen diffusion.