A galactose-specific lectin was purified from the skin mucus of African catfish (Clarias gariepinus) and the physicochemical properties determined. Phosphate buffered saline extract of the skin mucus of African catfish specifically agglutinated erythrocytes of rabbit and human blood group B, but did not agglutinate bat, rat, hen and human blood A and O erythrocytes. The haemagglutinating activity of the lectin was completely inhibited by lactose while galactose and melibiose inhibited the activity to some extent and was calcium-independent. The purified lectin has a native and subunit molecular weight of 63, 000 and 20, 000 Daltons, respectively suggesting a homotrimeric structure for the protein. The protein contained 126 amino acid residues per subunit. This was characterized by large amount of polar amino acids that constituted about 60% of the total amino acids. The lectin showed maximum activity over the pH range 6 – 9 and was heat stable up to 50°C. Ethylenediaminetetraacetic acid (EDTA) had no inhibitory effect on its haemagglutinating activity. Periodic acid–Schiff (PAS) staining showed that the lectin was not a glycoprotein. Chemical modifications of serine and arginine residues of the protein did not affect its haemagglutination activity while modifications of cysteine, tryptophan and histidine residues led to total loss of its activity. The study concluded that African catfish skin mucus lectin exhibited similar physicochemical properties with lectins from other fish skin mucus.

 

Key words: African catfish, Lectin, haemagglutination, skin mucus, galactose-specific, Clarias gariepinus