Glutathione complex with chromium

A. Levina and P. A. Lay, Solution structures of chromium(V) complexes with glutathione and model thiols, Inorg. Chem., 43 (2004) 324-335. 

However at neutral pH, solutions of chromium(VI) containing an excess of glutathione (1 10) rapidly develop a green colour,1454 which slowly decays to a purple colour typical of chromium(III) complexes. Concurrent with the green colour the typical EPR spectrum of a chromium(V) species is observed. Chromium(V) has also been observed in the EPR spectrum of frozen glasses obtained from reaction mixtures of chromium(VI) and glutathione.1455... 

Hexavalent chromium has no known essential function. However, trivalent chromium in the form of a dinicotinic acid-glutathione complex is an essential cofactor for insulin production and forms complexes with protein, amino acids, and other organic acids. 

P. O Brian, J. Pratt, F. J. Swanson, P. Thornton, and G. Wang, Chromium(V) containing complex from the reaction of glutathione with chromate, Inorg. Chim. Acta, 169 (1990) 265-269. 

It has been proposed that GTF is related to a dinicotinatotris(amino acid)chromium(III) complex, which forms a ternary complex at the membrane receptor with insulin. Porcine insulin binds a Cr(nic)2(glutathione) complex very tightly. 

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