Cloning, expression and characterization of a unique human liver microsomal glutathione-S-transferase

A unique human liver microsomal glutathione-S-transferase (GST) was purified to apparent electrophoretic homogeneity. Almost identical to a sheep liver microsomal GST purified just prior to this work, this basis human GST forms a 50.8 kDa homodimer composed of 25.4 kDa Ya-size subunits, and exhibits non-selenium dependent glutathione peroxidase activity towards organic hydroperoxides. The GST was cloned and expressed, and found to be encoded by an open reading frame 666 by in length. The recombinant GST had about 75% amino acid homology with the α-class cytosolic GSTs, but very little homology with the classic 51 kDa homotrimeric rat liver microsomal GST. All microsomal GSTs characterized prior to this work appear to be of independent evolutionary origin with respect to the cytosolic GSTs, based on low sequence homologies. The sheep and human liver microsomal GSTs discussed in this thesis, however, appear to represent a new and unique class of microsomal GSTs in that they display many features characteristic of cytosolic GSTs, most notably very high DNA and amino acid sequence homologies.