Role of the protein outside active site on the diffusion-controlled reaction of enzymes

1982 ◽  
Vol 104 (5) ◽  
pp. 1409-1413 ◽  
Author(s):  
Kuo Chen Chou ◽  
Guo Ping Zhou
Keyword(s):  
Active Site ◽  
Diffusion Controlled ◽  
Diffusion Controlled Reaction

Influence of counterion species on the dehydroxylation of Ca2+-, Mg2+-, Na+- and K+-exchanged Wyoming montmorillonite

2000 ◽  
Vol 64 (2) ◽  
pp. 337-346 ◽  
Author(s):  
H. J. Bray ◽  
S. A. T. Redfern
Keyword(s):  
Activation Energy ◽  
X Ray Diffraction ◽  
Interlayer Cation ◽  
Reaction Step ◽  
Octahedral Sheet ◽  
X Ray ◽  
First Order ◽  
Diffusion Controlled ◽  
Diffusion Controlled Reaction

AbstractThe dehydroxylation of Ca-, K-, Mg- and Na-saturated Wyoming montmorillonite has been studied by thermogravimetry (TG), infrared (IR) spectroscopy and X-ray diffraction (XRD). Samples saturated with either Ca2+ or Mg2+ show a predominantly diffusion-controlled reaction step, whereas Wyoming montmorillonite with Na+ and K+ in the interlayer exhibit control closer to first order. The activation energy of dehydroxylation is not significantly correlated to the type of interlayer cation present, in turn demonstrating that the role of vacancy location in the octahedral sheet is more significant a control on dehydroxylation.

scholarly journals The conserved cis-Pro39 residue plays a crucial role in the proper positioning of the catalytic base Asp38 in ketosteroid isomerase from Comamonas testosteroni

2003 ◽  
Vol 375 (2) ◽  
pp. 297-305 ◽  
Author(s):  
Gyu Hyun NAM ◽  
Sun-Shin CHA ◽  
Young Sung YUN ◽  
Yun Hee OH ◽  
Bee Hak HONG ◽  
...  
Keyword(s):  
Free Energy ◽  
Active Site ◽  
Crucial Role ◽  
Structural Integrity ◽  
Comamonas Testosteroni ◽  
Ketosteroid Isomerase ◽  
Free Energy Of Activation ◽  
Structural Rigidity ◽  
Diffusion Controlled

KSI (ketosteroid isomerase) from Comamonas testosteroni is a homodimeric enzyme that catalyses the allylic isomerization of Δ5-3-ketosteroids to their conjugated Δ4-isomers at a reaction rate equivalent to the diffusion-controlled limit. Based on the structural analysis of KSI at a high resolution, the conserved cis-Pro39 residue was proposed to be involved in the proper positioning of Asp38, a critical catalytic residue, since the residue was found not only to be structurally associated with Asp38, but also to confer a structural rigidity on the local active-site geometry consisting of Asp38, Pro39, Val40, Gly41 and Ser42 at the flexible loop between β-strands B1 and B2. In order to investigate the structural role of the conserved cis-Pro39 residue near the active site of KSI, Pro39 was replaced with alanine or glycine. The free energy of activation for the P39A and P39G mutants increased by 10.5 and 16.7 kJ/mol (2.5 and 4.0 kcal/mol) respectively, while ΔGUH2O (the free-energy change for unfolding in the absence of urea at 25.00±0.02 °C) decreased by 31.0 and 35.6 kJ/mol (7.4 and 8.5 kcal/mol) respectively, compared with the wild-type enzyme. The crystal structure of the P39A mutant in complex with d-equilenin [d-1,3,5(10),6,8-estrapentaen-3-ol-17-one], a reaction intermediate analogue, determined at 2.3 Å (0.23 nm) resolution revealed that the P39A mutation significantly disrupted the proper orientations of both d-equilenin and Asp38, as well as the local active-site geometry near Asp38, which resulted in substantial decreases in the activity and stability of KSI. Upon binding 1-anilinonaphthalene-8-sulphonic acid, the fluorescence intensities of the P39A and P39G mutants were increased drastically, with maximum wavelengths blue-shifted upon binding, indicating that the mutations might alter the hydrophobic active site of KSI. Taken together, our results demonstrate that the conserved cis-Pro39 residue plays a crucial role in the proper positioning of the critical catalytic base Asp38 and in the structural integrity of the active site in KSI.

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