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The active site consists of amino acid residues that form temporary bonds with the substrate, the binding site, and residues that catalyse a reaction of that substrate, the catalytic site. Although the active site occupies only ~10–20% of the volume of an enzyme, [ 1 ] : 19 it is the most important part as it directly catalyzes the chemical ...
Caspase-3 shares many of the typical characteristics common to all currently-known caspases. 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.
The active site can be characterized into two sub-sites denoted as S 1 ’ and S 1. The S 1 ’ sub-site is the hydrophobic pocket of the enzyme, and Tyr-248 acts to ‘cap’ the hydrophobic pocket after substrate or inhibitor is bound (SITE). [ 2 ]
Carboxypeptidases are usually classified into one of several families based on their active site mechanism. Enzymes that use a metal in the active site are called "metallo-carboxypeptidases" (EC number 3.4.17). Other carboxypeptidases that use active site serine residues are called "serine carboxypeptidases" (EC number 3.4.16).
The sophistication of the active site network causes residues involved in catalysis (and residues in contact with these) to be highly evolutionarily conserved. [62] However, many examples of divergent evolution in catalytic triads exist, both in the reaction catalysed, and the residues used in catalysis.
The triad is located in the active site of the enzyme, where catalysis occurs, and is preserved in all superfamilies of serine protease enzymes. The triad is a coordinated structure consisting of three amino acids : His 57, Ser 195 (hence the name "serine protease") and Asp 102.
Once appropriately dimerised, the Caspases cleave at inter domain linker regions, forming a large and small subunit. This cleavage allows the active-site loops to take up a conformation favourable for enzymatic activity. [15] Cleavage of Initiator and Executioner caspases occur by different methods outlined in the table below.
The active site also features a pocket suited for carbon dioxide, bringing it close to the hydroxide group. Kinetic studies performed determine the following mechanism for the enzyme: In Step 1 & 2, the nucleophile O − on the hydroxide ion coordinated to Zn 2+ performs a nucleophilic attack on the partially electrophilic carbon on the CO 2 ...