Acidic glutathione transferase from human heart: characterization and N-terminal sequence determination

The anionic glutathione transferase of human heart has been purified to homogeneity by using DEAE-cellulose, affinity chromatography, and FPLC. The enzyme has an isoelectric point at pH 4.75 and has an electrophoretic mobility on SDS-PAGE identical to placental transferase pi, indicating that the heart enzyme is formed by two similar subunits of 23,000 Mr. Upon isoelectric focusing on ampholine PAG plates the enzyme recovered from FPLC gave two bands of activity at pH 4.75 and 4.9 which were reduced to essentially a single band at pH 4.75 after incubation with dithiothreitol. In the immunodiffusion experiment, the heart enzyme gave a positive precipitin line with the antibodies against transferase pi but not with antibodies prepared against the "basic" transferase of human skin or against the "near-neutral" transferase of human uterus. The substrate specificities, the sensitivities to characteristic inhibitors, the amino acid composition, together with the immunological studies, strongly indicate that the anionic enzyme of human heart is closely related to the transferase pi of human placenta. The N-terminal amino acid sequence of the first 48 residues was determined and compared with the N-terminal region of other reported human glutathione transferase sequences. The heart enzyme differs from the placental enzyme in a single residue (Trp instead of Arg in the 28th position) further supporting their similarity.