Antigenic and Calcium Binding Properties of a Peptide Containing the Essential Cysteine in Lima Bean Lectin

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Abstract
Polyclonal antisera were raised against a peptide containing the cysteine residue required for carbohydrate binding activity in the lima bean lectin. The antisera were tested for cross-reactivity with (a) synthetic peptide analogs to the essential cysteine containing peptide, (b) proteolytic digests of related lectins, (c) native lectins. The antisera were specifically inhibited from binding to a peptide conjugate by free synthetic peptides. The degree of inhibition by lectin digests correlated approximately along evolutionary relationships and the degree of sequence conservation. One antiserum was found to cross-react with certain lectins in the native state. In a second set of experiments, the calcium binding properties of the synthetic peptides were investigated using metal ion-chelate chromatography and UV-difference spectroscopy. The nonapeptide and undecapeptide bound to a Ca2+ iminodiacetic acid agarose column and were eluted with EDTA. Ultraviolet difference spectral titrations with Ca2+ performed on the synthetic undecapeptide and a related favin derived peptide resulted in dissociation constants of approximately 6 × 103 per molar.