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Pakistan Journal of Biological Sciences
Year: 2006  |  Volume: 9  |  Issue: 4  |  Page No.: 674 - 680

Studies on the Chemical Modification of Mulberry Seed Lectin (MSL-1) and its Effect on Hemagglutinating Activity

M.A. Hossain, M.T. Hossain and N. Absar    

Abstract: The lectin, MSL-1 was subjected to various chemical modifications in order to ascertain the amino acid residues responsible for their hemagglutinating activity. Modification of MSL-1 with acetic anhydride blocked nineteen amino groups and five tyrosine residues per molecule of lectin and decreased complete hemagglutinating activity. De-O-acetylation regenerated four of the tyrosine residues and resulted in a recovery of 80% activity. The presence of inhibitory saccharide galactose, a significant protecting effect was observed and only 1.49 tyrosine residues and fifteen amino groups were found to be modified with significant retention of hemagglutinating activity. The treatment of lectin with citraconic anhydride showed that nineteen amino were modified with the loss of 25-30% hemagglutinating activity. Modification of lectin with N-acetyl imidazole resulted in acetylation of fifteen amino groups and six tyrosine residues per molecule. De-O-actylation also regenerated 4.5 tyrosine residues with the retention of 75% of its hemagglutinating activity. When modification was conducted in the presence of galactose, about 3.5 tyrosine residues were protected from modification with 80% hemagglutinating activity. Successive addition of NBS to MSL-1 solution resulted in the modification of five tryptophan residues per molecule of lectin at pH 6, 5 and 4, respectively with the loss of 20-30% hemagglutinating activity. With DEPC at pH 7.2, eight histidine residues were modified and in the presence of inhibitory saccharide galactose, five histidine residues were protected from modification with the retention of 90% hemagglutinating activity. This was further confirmed from the finding that the activity was regenerated when His-modified MSL-1 was treated with hydroxylamine. The overall modification studies indicated that four tyrosine and five histidine residues were located at the saccharide-binding site of the lectin. However, modification of tryptophan and lysine had no effect on the hemagglutinating activity.

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