The existence of this seventh catalytic type of proteases, in which the peptide bond cleavage occurs by self-processing instead of hydrolysis, was demonstrated with the discovery of the crystal structure of the self-cleaving precursor of the Tsh autotransporter from " E . coli ".
32.
This induces the enzyme to change its conformation, and creates a binding site for the acetyl-CoA . Only when this citroyl-CoA has formed will another conformational change cause thioester hydrolysis and release coenzyme A . This ensures that the energy released from the thioester bond cleavage will drive the condensation.
33.
For example, its active site contains a cysteine residue ( Cys-163 ) and histidine residue ( His-121 ) that stabilize the peptide bond cleavage of a protein sequence to the carboxy-terminal side of an aspartic acid when it is part of a particular 4-amino acid sequence.
34.
In reactions with polar mechanisms, Lewis acid catalysis often involves binding of the catalyst to Lewis basic heteroatoms and withdrawing electron density, which in turn facilitates heterolytic bond cleavage ( in the case of Friedel-Crafts reaction ) or directly activates the substrate toward nucleophilic attack ( in the case of carbonyl addition reactions ).
35.
Generally, with catenation comes the loss of the total amount of bonded hydrocarbons and an increase in the amount of energy required for bond cleavage due to strain exerted upon the molecule; in molecules such as cyclohexane, this is referred to as ring strain, and occurs due to the " destabilized " spatial electron configuration of the atom.
36.
Control in RAFT polymerization ( scheme 1 ) is achieved in a far more complicated manner than the homolytic bond formation-bond cleavage of SFRP and ATRP . The CTA for RAFT polymerization must cautiously chosen because it has an effect on polymer length, chemical composition, rate of the reaction and the number of side reactions that may occur.
37.
So I " think " the only time you need to use the term " phosphoesterase " or " metallophosphoesterase " is when you deliberately want to leave it ambiguous whether the ester bond cleavage releases a free phosphate + O-R or a bound phosphate + O-R . This might be due to describing a whole superfamily of related enzymes, or if an enzyme's activity is as yet uncharacterized, or if it does both things to some degree . talk ) 21 : 04, 11 October 2010 ( UTC)
