Glutathione-S-transferase activity from rat placenta.

Glutathione S-transferase activity significantly decreased in the rat placenta from the 16th to the 20th day of gestation. Isoelectric focusing of rat placenta supernatant yielded essentially a single peak of glutathione S-transferase activity with I-chloro-2,4-dinitrobenzene as substrate, centred on pH 7.45. Substrate specificity measurements, as well as inhibitory studies, revealed pronounced differences between rat and human placental enzymes. Whether the biochemical differences between rat and human GSH-Trs are reflected in physiological differences remains to be ascertained. The sodium dodecyl sulphate (SDS) gel electrophoresis data on subunit composition showed that the rat enzyme is composed of two identical subunits whose molecular mass closely approaches that of human transferase.