Mn²⁺-electron spin resonance spectra of several lectins

Mn²⁺-ESR spectra of soybean, wax bean and lima bean agglutinin at Q- and X-band frequencies show nearly axially symmetric zero field splitting (ZFS); the dominant anisotropic term of the spin hamiltonian is the quadratic ZFS interaction. There is a relatively large distribution of ZFS parameters. No effects of specific inhibitor (N-acetylgalactosamine) on the soybean agglutinin spectrum were observed. The stoichiometric complex obtained on addition of Mn²⁺ to a Mn²⁺-free sample of this protein has a spectrum similar to that of the native protein. The small changes in the spectrum are interpreted in terms of a wider distribution of the ZFS parameters at the Mn binding site. Addition of Ca²⁺ to Mn²⁺-soybean agglutinin sharpens the lines, possibly because Ca²⁺ increases the rigidity of the complex.