title: A reinvestigation of the mechanism of Pseudomonas testosteroni delta 5-3-ketosteroid isomerase.
abstract: The mechanism of the isomerisation of delta 5-3,17-androstenedione by the isomerase (3-oxosteroid delta 4-delta 5-isomerase, EC 5.3.3.1) of Pseudomonas testosteroni has been reinvestigated with delta 5-[4-beta-2H]androstenedione as substrate in H2O and delta 5-androstenedione in 2H2O. A precise localisation of the label in delta 4-androstenendione has  revealed that the previously reported 4 beta leads to 6 beta deuterium transfer accounts for only a part of the reaction. Along with this process, removal of the 4 alpha proton is also occurring. This has already been observed with mammalian isomerases. Hence the assumed difference in mechanism between the bacterial and mammalian enzymes is very unlikely.
mesh_terms: D000735:Androstenedione; D003903:Deuterium; D007535:Isomerases / Q000378:metabolism*; D007553:Isotope Labeling; D011549:Pseudomonas / Q000201:enzymology*; D013251:Steroid Isomerases / Q000378:metabolism*
chemical_list: D000735:Androstenedione; D003903:Deuterium; D007535:Isomerases; D013251:Steroid Isomerases