Liganded and unliganded forms of Antarctic fish haemoglobins in polyethylene glycol: crystallization of an R-state haemichrome intermediate

Liganded and unliganded forms of two Antarctic fish haemoglobins, from Trem atomus newnesi and T. bernacchii, have been crystallized in low-salt media using polyethylene glycol as precipitant. In particular, crystals of air-ex posed T. newnesi carbomonoxy haemoglobin were found to be isomorphous to th e crystals grown in high-salt media. Preliminary X-ray analysis of the diff raction data revealed that the beta -haem iron of this haemoglobin is in th e haemichrome state, with both the proximal and distal histidyl residues li nked to the iron. This is the first crystallization of a haemichrome interm ediate of a vertebrate haemoglobin.