title: Regulation by progesterone and pregnenolone of dimeric aldehyde dehydrogenase from rat testis cytoplasm.
abstract: 1. Aldehyde dehydrogenase from rat testis cytosol has been purified to electrophoretic homogeneity. With an isoelectric point of 9.5, the enzyme appears a dimer with a subunit molecular weight of 52,500. 2. The influence of pregnenolone and progesterone on the kinetic behaviour has been investigated using valeraldehyde as substrate. 3. The kinetic data were fitted to a modified version of the Monod-Wyman-Changeux model and the fitting procedure resulted in a good correspondence between theoretical and experimental reaction rates over a wide range of valeraldehyde concentrations. 4. According to the model, the dimeric enzyme is in equilibrium between two conformational states R and T. The R state displays higher affinity for valeraldehyde, but lower catalytic power. In the absence of substrates and effectors the [T]/[R] ratio is near to 1. 5. Pregnenolone and progesterone activate the enzyme by stabilizing the more active state T and by increasing the catalytic power of the R state. The increase of activity is counteracted by the inhibition exerted by both steroids on the T state.
authors.affiliation: Dipartimento di Medicina e Oncologia, Sperimentale, Università di Torino, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Bedino
authors.forename: G
authors.initials: G
authors.lastname: Testore
mesh_terms: D000444:Aldehyde Dehydrogenase / Q000737:chemistry / Q000187:drug effects* / Q000302:isolation & purification; D000818:Animals; D001704:Biopolymers; D003593:Cytoplasm / Q000201:enzymology*; D004795:Enzyme Stability; D008297:Male; D008956:Models, Chemical; D008970:Molecular Weight; D011284:Pregnenolone / Q000494:pharmacology*; D011374:Progesterone / Q000494:pharmacology*; D051381:Rats; D013737:Testis / Q000201:enzymology* / Q000648:ultrastructure
chemical_list: D001704:Biopolymers; D011374:Progesterone; D011284:Pregnenolone; D000444:Aldehyde Dehydrogenase