The rate of formation of transition-state analogs in the active site of adenosine deaminase is encounter-controlled: implications for the mechanism

Biochemistry ◽  
1992 ◽  
Vol 31 (1) ◽  
pp. 39-48 ◽  
Author(s):  
Linda C. Kurz ◽  
Luke Moix ◽  
Marian C. Riley ◽  
Carl Frieden
Keyword(s):  
Transition State ◽  
Adenosine Deaminase ◽  
Active Site ◽  
Transition State Analogs

An allolactose trapped at the lacZ β-galactosidase active site with its galactosyl moiety in a 4H3 conformation provides insights into the formation, conformation, and stabilization of the transition state

2015 ◽  
Vol 93 (6) ◽  
pp. 531-540 ◽  
Author(s):  
Robert W. Wheatley ◽  
Reuben E. Huber
Keyword(s):  
Transition State ◽  
Active Site ◽  
Axial Position ◽  
Transition State Analog ◽  
X Ray ◽  
Transition State Analogs ◽  
Leaving Group ◽  
Sugar Ring ◽  
Oxocarbenium Ion ◽  
Ring Distortion

When lactose was incubated with G794A-β-galactosidase (a variant with a “closed” active site loop that binds transition state analogs well) an allolactose was trapped with its Gal moiety in a 4H3 conformation, similar to the oxocarbenium ion-like conformation expected of the transition state. The numerous interactions formed between the 4H3 structure and β-galactosidase indicate that this structure is representative of the transition state. This conformation is also very similar to that of d-galactono-1,5-lactone, a good transition state analog. Evidence indicates that substrates take up the 4H3 conformation during migration from the shallow to the deep mode. Steric forces utilizing His418 and other residues are important for positioning the O1 leaving group into a quasi-axial position. An electrostatic interaction between the O5 of the distorted Gal and Tyr503 as well as C–H–π bonds with Trp568 are also significant. Computational studies of the energy of sugar ring distortion show that the β-galactosidase reaction itinerary is driven by energetic considerations in utilization of a 4H3 transition state with a novel 4C1-4H3-4C1 conformation itinerary. To our knowledge, this is the first X-ray crystallographic structural demonstration that the transition state of a natural substrate of a glycosidase has a 4H3 conformation.

Active-site-directed specific competitive inhibitors of phospholipase A2: novel transition-state analogs

Biochemistry ◽  
1991 ◽  
Vol 30 (42) ◽  
pp. 10256-10268 ◽  
Author(s):  
Mahendra Kumar Jain ◽  
Weijing Tao ◽  
Joe Rogers ◽  
C. Arenson ◽  
H. Eibl ◽  
...  
Keyword(s):  
Transition State ◽  
Phospholipase A2 ◽  
Active Site ◽  
Transition State Analogs ◽  
Competitive Inhibitors
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