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Considerable interest is currently focused on fish haemoglobins in order to identify the structural basis for their diversity of functional behaviour. The armored catfish Lip osarcus anisitsi presents accessorial air breathing through a modified stomach, which allows this species to survive in waters with low oxygen content. The analysis of its haemolysate has shown the presence of four main haemoglobins, with this work focusing on haemoglobin IV (LaHb-IV). LaHb-IV was crystallized and X-ray diffraction data were collected to 2.4 Å resolution using a synchrotron-radiation source. The crystal belongs to the orthorhombic space group P212121, with unit-cell parameters a = 52.6 (1), b = 104.8 (2), c =113.9 (2) Å; preliminary structural analysis revealed the presence of one tetramer in the asymmetric unit. The structure was determined using the standard molecular-replacement technique. [ABSTRACT FROM AUTHOR]

Haemoglobin, the `honorary enzyme' [Brunori (1999), Trends Biochem. Sci. 24, 158-161], constitutes a prime prototype for allosteric models. Here, the crystallization and preliminary X-ray analysis of haemoglo bin I from the South American fish Brycon cephalus are reported. X-ray diffraction data have been collected to 2.5 Å resolution using synchrotron radiation (LNLS). Crystals were determined to belong to the space group P6122 and preliminary structural analysis revealed the presence of one dimer (αβ) in the asymmetric unit. The structure was determined using standard molecular-replacement techniques. [ABSTRACT FROM AUTHOR]

Liposarcus anisitsi is an armoured catfish that presents accessorial air oxygenation through a modified stomach, which allows this species to survive in waters with very low oxygen content. Analysis of its haemolysate has shown the presence of four haemoglobins; this work focuses on the main component, haemoglobin I. It has been crystallized in two different forms and X-ray diffraction data have been collected to 2.77 and 2.86 Å resolution using synchrotron radiation. Crystals were determined to belong to the space groups C2 and P21 and preliminary structural analysis revealed the presence of one tetramer in the asymmetric unit in both crystal forms. The structure was determined using a standard molecular-replacement technique. [ABSTRACT FROM AUTHOR]