Efficient reduction of Cys110 thiyl radical by glutathione in human myoglobin.

Human myoglobin (hMb) possesses a cysteine (Cys) residue which is rare among mammalian Mbs. To investigate the effects of this unique Cys residue at the amino acid position 110 (Cys110) on hMb reactions, we studied the reactions of wild type (WT) methMb and its alanine mutant at Cys110 (C110A) with H(2)O(2), particularly in the presence of reduced glutathione (GSH) which is well known as a reducing agent. The formation rates of the ferryloxo (Fe(IV)=O) species by H(2)O(2) under air were about the same for WT and C110A methMbs, whereas the protein decomposed more in the case of WT than C110A hMb. With the addition of GSH, hMb consumed H(2)O(2) faster and decomposition of the protein decreased, where the effects were more prominent in WT than C110A hMb. The radicals produced by the reaction with H(2)O(2) decreased significantly due to the addition of 1mM GSH in the case of WT hMb, but not in the case of C110A hMb. These results show that GSH reduces H(2)O(2)-induced protein decomposition due to reduction of the C110-thiyl radical in WT hMb by electron transfer.