Electron Paramagnetic Resonance and Magnetic Susceptibility Studies of Dimanganese Concanavalin A. Evidence for Antiferromagnetic Exchange Coupling

Bradley C. Antanaitis, Seymour H. Koenig, N. Dennis Chasteen, C. Fred Brewer, Rodney D. Brown, Henry R. Lilienthal, Jonathan H. Freedman, Jack Peisach

Research output: Contribution to journalArticle

32 Scopus citations

Abstract

The double Mn2+ complex of concanavalin A with bound saccharide (SMMPL) was examined by electron paramagnetic resonance (EPR) spectroscopy and magnetic susceptibility measurements. A room temperature X-band (9 GHz) EPR spectrum of SMMPL revealed a relatively weak, broad resonance in contrast to the spectrum with a six-line hyperfine-split pattern observed for the mononuclear, high-spin Mn2+ complex found in Ca2+-Mn2+-concanavalin A with saccharide present (SCMPL). The EPR spectrum of SMMPL at 77 K, however, consisted of a series of overlapping patterns of 11 hyperfine-split lines near g = 2.0 with members of each pattern separated by 47 G, half the value of the hyperfine splitting of SCMPL. These 11-line patterns are preserved at Q-band (35 GHz), indicating that the manganese ions in SMMPL form a spin-coupled, binuclear center. As expected for an exchange-coupled system, the EPR signal of SMMPL at 77 K saturates at a higher microwave power than those for SCMPL or Mn2+ aquoion. There is also a marked loss of EPR signal intensity for SMMPL between 4.2 and 1.4 K, which supports the view that the pair of manganese ions is exchanged-coupled. The temperature dependence of both the magnetic susceptibility and the low-temperature EPR spectral intensity can be explained by a model in which the two high-spin Mn2+ ions of SMMPL are antiferromagnetically-exchanged-coupled with an isotropic coupling constant J = 1.8 cm-1(for the spin Hamiltonian Hex - JS1.S2). Zero-field splitting D’ was estimated to be 375 G from the EPR spectrum. The results provide direct evidence for coupled Mn2+ ions in the SMMPL complex, which is consistent with their binding at the S1 and S2 sites in the protein.

Original languageEnglish (US)
Pages (from-to)7932-7937
Number of pages6
JournalBiochemistry
Volume26
Issue number24
DOIs
StatePublished - 1987

ASJC Scopus subject areas

  • Biochemistry

Fingerprint Dive into the research topics of 'Electron Paramagnetic Resonance and Magnetic Susceptibility Studies of Dimanganese Concanavalin A. Evidence for Antiferromagnetic Exchange Coupling'. Together they form a unique fingerprint.

  • Cite this

    Antanaitis, B. C., Koenig, S. H., Chasteen, N. D., Brewer, C. F., Brown, R. D., Lilienthal, H. R., Freedman, J. H., & Peisach, J. (1987). Electron Paramagnetic Resonance and Magnetic Susceptibility Studies of Dimanganese Concanavalin A. Evidence for Antiferromagnetic Exchange Coupling. Biochemistry, 26(24), 7932-7937. https://doi.org/10.1021/bi00398a058