Low-molecular-weight chromium-binding substance

Nature of binding

From spectroscopic data, it has been shown that Cr3+ binds tightly to chromodulin (Kf = 1021 M−4), and that the binding is highly cooperative (Hill Coefficient = 3.47). Chromodulin is highly specific for Cr3+ as no other metals are able to stimulate tyrosine kinase activity. It is believed to stimulate the phosphorylation of the 3 tyrosine residues of the β subunits of the insulin receptor. From electronic studies, the crystal field stabilization energy was determined to be 1.74 x 103 while the Racah parameter B was 847 cm−1. This indicates that chromium binds to chromodulin in the trivalent form. In addition, magnetic susceptibility studies have shown that chromium does not coordinate to any N-terminal amine groups but rather to carboxylates (although the exact amino acids involved are still unknown). These magnetic susceptibility studies are consistent with the presence of a mononuclear Cr3+ center and an unsymmetric trinuclear Cr3+ assembly with bridging oxo ligands. In chromodulin isolated from bovine liver, x-ray absorption spectroscopy studies have shown that the chromium (III) atoms are surrounded by 6 oxygen atoms with an average Cr—O distance of 1.98 Å, while the distance between 2 chromium (III) atoms is 2.79 Å. These results are indicative of a multinuclear assembly. No sulfur ligands coordinate to chromium and instead, it has been proposed that a disulfide linkage between 2 cysteine residues occurs owing to a characteristic peak at 260 nm.

References

References

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