Biomaterial Database

Energetics of 3-oxo-delta 5-steroid isomerase: source of the catalytic power of the enzyme. 1991

D C Hawkinson, and T C Eames, and R M Pollack

Department of Chemistry and Biochemistry, University of Maryland Baltimore County 21228-5398.

Knowledge of the partitioning of the putative dienol intermediate (2) by steroid isomerase (KSI) (Hawkinson et al. 1991), in conjunction with various steady-state kinetic parameters, allows elucidation of the detailed free energy profile for the KSI-catalyzed conversion of 5-androstene-3,17-dione (1) to 4-androstene-3,17-dione (3). This free energy profile shows four kinetically significant energy barriers (substrate binding, the two chemical steps, and dissociation of product) that must be traversed upon conversion of 1 to 3. Thus, no single step of the catalytic cycle is cleanly rate-limiting. The source of the catalytic power of KSI is discussed via comparison of the free energy profile for the KSI-catalyzed isomerization with those for the acetate-catalyzed isomerization and the aqueous reaction at pH 7. Similarities between the energetics of the KSI-catalyzed and triosephosphate isomerase catalyzed reactions are also noted.

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008433	Mathematics	The deductive study of shape, quantity, and dependence. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)	Mathematic
D008962	Models, Theoretical	Theoretical representations that simulate the behavior or activity of systems, processes, or phenomena. They include the use of mathematical equations, computers, and other electronic equipment.	Experimental Model,Experimental Models,Mathematical Model,Model, Experimental,Models (Theoretical),Models, Experimental,Models, Theoretic,Theoretical Study,Mathematical Models,Model (Theoretical),Model, Mathematical,Model, Theoretical,Models, Mathematical,Studies, Theoretical,Study, Theoretical,Theoretical Model,Theoretical Models,Theoretical Studies
D011549	Pseudomonas	A genus of gram-negative, aerobic, rod-shaped bacteria widely distributed in nature. Some species are pathogenic for humans, animals, and plants.	Chryseomonas,Pseudomona,Flavimonas
D002151	Calorimetry	The measurement of the quantity of heat involved in various processes, such as chemical reactions, changes of state, and formations of solutions, or in the determination of the heat capacities of substances. The fundamental unit of measurement is the joule or the calorie (4.184 joules). (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)
D000735	Androstenedione	A delta-4 C19 steroid that is produced not only in the TESTIS, but also in the OVARY and the ADRENAL CORTEX. Depending on the tissue type, androstenedione can serve as a precursor to TESTOSTERONE as well as ESTRONE and ESTRADIOL.	4-Androstene-3,17-dione,delta-4-Androstenedione,4 Androstene 3,17 dione,delta 4 Androstenedione
D013251	Steroid Isomerases	Enzymes that catalyze the transposition of double bond(s) in a steroid molecule. EC 5.3.3.	3-Ketosteroid Isomerases,3-Oxosteroid Isomerases,3 Ketosteroid Isomerases,3 Oxosteroid Isomerases,Isomerases, 3-Ketosteroid,Isomerases, 3-Oxosteroid,Isomerases, Steroid
D013816	Thermodynamics	A rigorously mathematical analysis of energy relationships (heat, work, temperature, and equilibrium). It describes systems whose states are determined by thermal parameters, such as temperature, in addition to mechanical and electromagnetic parameters. (From Hawley's Condensed Chemical Dictionary, 12th ed)	Thermodynamic