ESR studies on the effect of ionic radii on displacement of Mn2+ bound to a soluble β‐galactoside binding hepatic lectin

[摘要]

Binding of divalent metal ions to hepatic soluble β-galactoside binding lectin was studied using electron spin resonance (ESR) spectroscopy. The Mn²⁺ bound to hepatic lectin could be displaced by Mg²⁺, Cu²⁺, Ni²⁺ and Ca²⁺ but not by Sr²⁺. As the ionic radii of Mg²⁺ (0.65 Å), Cu²⁺ (0.73 Å) and Ni²⁺ (0.72 Å) are appreciably smaller than Ca Mn²⁺ binding site is more accessible to Mg²⁺, Cu²⁺, and Ni²⁺ as compared to Ca²⁺, the ionic radius of Mn²⁺ being 0.80 Å. Sr²⁺ with an ionic radius of 1.13 is thus unable to displace bound Mn²⁺. Surprisingly, the presence of specific sugars like α-lactose, or α-d-galactose facilitated the displacement of bound Mn²⁺ by metal ions whereas non-specific sugars, i.e. α-d-glucose, β-d-fructose and α-d-ribose had no effect. It appears that minor perturbations in the saccharide binding site significantly affect the ability of the metal binding site to ligate bivalent metals.

[学科分类] 生物化学/生物物理

[关键词] β-Galactoside binding lectin;Metal binding;EPR