A potential mechanism by which α-tocopherol maintains oxymyoglobin pigment through cytochrome b₅ mediated reduction

The effect of α-Tocopherol (α-Toc) on the reduction of metmyoglobin (MetMb) was investigated using a liver extract containing cytochrome b₅ (LE) prepared from bovine liver in a Triton X-100 system at 37°C and at pH 7·2, 6·2, and 5·6, The combination of α-Toc and LE reduced Met Mb at pH 5·6 and pH 6·2 (p < 0·05), but not at pH 7·2, When LE was added, substitution of α-Toc with gtutathione (0·15 μM) resulted in 13% MetMb reduction, a rate similar to α-Toc plus LE (pH 5·6). The addition of NADH and NADPH with LE at pH 5·6 resulted in MetMb reduction of 85% and 25%, respectively, relative to controls. α-Toc-mediated reduction at pH 5·6 was further investigated using a purified bovine liver cytochrome b₅ (Cyt b₅). α-Toc effectively reduced Cyt b₅, as indicated by an increased absorbance at 424 nm. The combination of α-Toc plus purified Cyt b₅ resulted in a 15% reduction in MetMb at pH 5·6 (p<0·05) relative to controls. These results suggested a potential reaction whereby α-Toc maintains OxyMb via enhancement of Cyt b₅-mediated reduction of MetMb.