Heterogeneity and subunit composition of the haemoglobins of five tilapiine species (Teleostei, Cichlidae) of the genera Oreochromis and Sarotherodon.

Haemoglobins of five tilapiine species of the genera Oreochromis and Sarotherodon were investigated. By gel filtration chromatography a molecular weight of 67-69 kDa was determined for the tetrameric molecules which remained stable between pH 5.0 and pH 9.1. When subjected to sodium dodecyl sulphate-Ureapolyacrylamide gel electrophoresis (PAGE), haemoglobins of all species each were split into monomers of three different molecular weights ranging between 16.3 kDA and 17.6 kDa. Subsequently, isoelectric focusing separated haemolysates into about 23 differently charged tetrameric haemoglobins that were arranged in species-specific patterns. This diversity was shown to result from the occurrence of different types of globin chains. By acidic urea PAGE a total of seven major alpha-globins and five major beta-globins were detected and species-characteristic chain variants were identified. To determine the globin chain composition of particular haemoglobin tetramers, 26 bands were isolated by isoelectric focusing and analysed by acidic urea PAGE. Tetramers consisted of doublets of identical alpha- and identical beta-chains (alpha 2 beta 2, symmetric tetramers), or combinations of three (alpha 2 beta beta *; alpha alpha * beta 2) or four (alpha alpha * beta beta *) distinct chains (asymmetric tetramers). Finally, globin chains of Oreochromis niloticus were subjected to partial N-terminal amino acid sequencing. Differences in the composition of the three major beta-chains could be shown, whereas the alpha-chains were N-terminally blocked.