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A study conducted on the crystal structure of the human quinone reductase type 2 (QR2) revealed the existence of two separate but homologous cytosolic quinone reductases. One is NAD(P)H: quinone reductase type 1 (QR1) and QR2. QR1 has been found to be involved in the catabolism of xenobiotics. Both QR2 and QR1 have the same overall fold of their major catalytic domains, but QR2 lacks the smaller C-terminal domain. The FAD binding sites of the two were also found to be similar except for their hydride donor binding site, which was found to be absent in QR1.

The influence of Asp-99 and Tyr-14 in the catalysis of ketosteroid isomerase was determined through the use of 3D 1H-13C NOESY-HSQC spectrum of Tyr-14 mutant isomerase and UV resonance Raman spectroscopy. The H-bond donation by Tyr-14 was compensated by another H-bond donor. The side chain of Asp-99 was characterized to be proximal to the aromaric ring of Tyr-14. Asp-99 donation of H-bond was stronger that that of Tyr-14, confirming the importance of Asp and Tyr residues in the formation of H-bonds on enzymes.

The secondary structure, in solution, of the Y55F/Y88F highly active mutant of isomerase, when complexed with 19-nortestosterone hemisuccinate, has been determined. The results of heteronuclear NMR studies showed two alpha-helices, one 3(sub 10) helix, seven beta-strands, and five turns. The isomerase, therefore, consists of 30% helix, 38% beta-sheet and 16% turns. The remaining 20 residues (16 %) are assumed to form coils.

The side chain and backbone dynamics of the catalytic residue, Tyr-14, in free and steroid-bound delta-5-3-ketosteroid isomerase were studied by determining the longitudinal and transverse 13C relaxation rates and nuclear Overhauser effects at both 500 and 600 MHz proton frequencies. Findings indicated that the amplitude of the high-frequency side chain movement of Tyr-14 was more restricted in the steroid complex compared to its backbone.

The polarization state of the bond between the Tyr-14 residue and the substrate of the enzyme delta5-3-ketosteroid isomerase is intermediate between proton donation and a hydrogen bond. The Tyr-14 residue stabilizes the 3-carbonyl group and the Asp-38 residue removes a proton from the steroid ring. A compensating hydrogen bond could be provided by a water molecule or a backbone amide NH.

UV and fluorescence spectroscopy help analyze the influence of solvent on enzymatic and nonenzymatic polarizations of ketosteroid and phenolic steroids, upon binding to the active site of Delta(5)-3-keto-steroid isomerase of Pseudomonas testosteroni. Spectral changes of these steroids upon binding to the active sites are explained by strong, directional hydrogen bonding between the steroid ligands and Tyr-14. These strong, low-barrier hydrogen bonds account for the spectral changes observed during the catalysis of Delta(5)-3 ketosteroid isomerase.

The 4Cl-phenacyl methyl phosphonates hydrolyze rapidly, but are efficient inhibitors of serene-hydrolase enzymes trypsin and alpha-chymotrypsin due to the favorable interaction of phenacyl group in the phosphonates with the binding pocket in the substrate. The carbonyl hydrate-promoted reactivation procedure is inhibited by the formation of oxyphosphorane, resulting in regeneration of enzyme activity.

Reports effects of the medium on the UV and fluorescence spectral properties of alpha, beta-unsaturated ketosteroids and phenolic compounds. Comparison of these properties to those of enzyme-bound steroids; Experimental procedures, results and discussion; Explanation of spectral findings by strong, directional hydrogen bonding interaction between Tyr-14 and steroid ligands in solvent-inaccessible active site.