Purification and Properties of S-Formylglutathione Hydrolase from Human Liver

Abstract

Abstract S-Formylglutathione hydrolase, a new glutathione thiol esterase from human liver, has been purified into homogeneity according to disc electrophoretic and ultracentrifugal criteria. The final preparation catalyzes the hydrolysis of 4100 µmoles of S-formylglutathione per min per mg of protein at 25° and represents 2,350-fold purification over 23,000 x g supernatant of liver homogenate. In addition to S-formylglutathione, the enzyme can catalyze the hydrolysis of S-acetylglutathione at a 200-fold slower velocity but has no activity with S-lactylglutathione. The elution volume of the enzyme in a gel filtration column gives an apparent molecular weight of 52,500 and a diffusion coefficient of 6.57 x 10-7 cm2 s-1. The enzyme has a sedimentation coefficient of 4.24 S as judged from sedimentation velocity in analytical ultracentrifuge. From a sedimentation equilibrium experiment, the molecular weight of the enzyme is 55,500. Dodecyl sulfate gel electrophoresis indicates a subunit molecular weight of 30,000. Thus, the enzyme probably consists of 2 subunits. The isoelectric point of the enzyme obtained from electrofocusing experiments is 5.41. The enzyme apparently contains a reactive —SH group and purification is possible only in the presence of thiols. Activity is rapidly lost when the thiols are removed, but dithiothreitol can regenerate part of the activity. Several types of —SH reagents are inhibitory. Dithiothreitol can reverse completely the effect of mercaptide-forming and oxidizing agents. Amino group reagents also rapidly inactivate the enzyme. In addition, ascorbate and folate are inhibitory. Chelating agents and organophosphates do not inhibit the enzyme.