Differences between bovine and human steroid double-bond isomerase activities of Alpha-class glutathione transferases selectively expressed in steroidogenic tissues
2007 (English)In: Biochimica et Biophysica Acta - General Subjects, ISSN 0304-4165, E-ISSN 1872-8006, Vol. 1770, no 1, 130-136 p.Article in journal (Refereed) Published
Bovine glutathione transferase A1-1 (bGST A1-1) and human GST A3-3 (hGST A3-3) share both high amino acid sequence similarity and selective expression in steroidogenic organs. hGST A3-3 is the most efficient steroid isomerase known in mammals, and is thought to catalyze isomerization reactions in the biosynthesis of steroid hormones. We observed that four out of five residues essential to the high steroid isomerase activity of hGST A3-3 are conserved in bGST A1-1. The bovine GST was cloned, heterologously expressed, and purified to homogeneity. Its specific activity towards classical GST substrates and two steroids, Delta(5)-androstene-3,17-dione and Delta(5)-pregnene-3,20-dione, was studied, and the steady-state kinetic parameters with the steroids were determined. We find that bGST A1-1 exhibits enzymatic activities comparable to those of hGST A3-3 towards non-steroid substrates. However, the bovine enzyme had 100 times lower catalytic efficiency in steroid isomerization reactions than the human GST. Nevertheless, bGST A1-1 was found as efficient as bovine 3 beta-hydroxysteroid dehydrogenase as a steroid isomerase. We discuss likely reasons for the contrasting steroid isomerase activities of bGST AM and hGST A3-3, and alternative roles of bGST A1-1.
Place, publisher, year, edition, pages
2007. Vol. 1770, no 1, 130-136 p.
alpha-class glutathione transferases, bovine GST Al-1, steroid double-bond isomerase, steroidogenesis, steroidogenic organ
Biochemistry and Molecular Biology
IdentifiersURN: urn:nbn:se:uu:diva-146489DOI: 10.1016/j.bbagen.2006.06.015ISI: 000243631600018PubMedID: 16934407OAI: oai:DiVA.org:uu-146489DiVA: diva2:398277