Active site 188688 225128201 2008-07-12T00:51:49Z 132.216.68.137 /* Models */ corrected "...substrate. After which..." for grammar The '''active site''' of an [[enzyme]] contains the [[catalysis|catalytic]] and [[binding sites]]. The structure and chemical properties of the active site allow the recognition and binding of the [[substrate (biochemistry)|substrate]]. The active site is usually a small pocket at the surface of the [[enzyme]] that contains residues responsible for the substrate specificity (charge, hydrophobicity, steric hindrance) and catalytic residues which often act as proton donors or acceptors or are responsible for binding a cofactor such as [[Pyridoxal phosphate|PLP]], [[Thiamine pyrophosphate|TPP]] or [[Nicotinamide adenine dinucleotide|NAD]]. The active site is also the site of inhibition of enzymes (see [[Enzyme inhibitor]] article). ==Models== There are two proposed models of how enzymes work: the lock-and-key model and the [[Enzyme catalysis#Induced fit|induced fit]] model. The lock-and-key model assumes that the active site is a perfect fit for a specific substrate and that once the substrate binds to the enzyme no further modification is necessary, this is simplistic. The induced fit model is a development of the lock and key model and instead assumes that an active site is more flexible and that the presence of certain residues (amino acids) in the active site will encourage the enzyme to locate the correct substrate, after which conformational changes may occur as the substrate is bound. Substrates bind to the active site of the enzyme or a specificity pocket through hydrogen bonds, hydrophobic interactions, temporary covalent bonds (van der waals) or a combination of all of these to form the enzyme-substrate complex. Residues of the active site will act as donors or acceptors of protons or other groups on the substrate to facilitate the reaction. In other words, the active site modifies the reaction mechanism in order to decrease the activation energy of the reaction. The product is usually unstable in the active site due to steric hindrances that force it to be released and return the enzyme to its initial unbound state. ==See also== * [[Enzyme catalysis]] * [[Hugh Stott Taylor]] * [[Catalytic triad]] * [[Activity based proteomics]] {{Enzymes}} [[Category:Enzymes]] {{enzyme-stub}} [[es:Sitio activo]] [[fr:Site actif]] [[it:Sito attivo]] [[he:אתר פעיל]] [[pl:Centrum aktywne]] [[ru:Активный центр ферментов]] [[sl:Aktivno mesto encima]] [[uk:Активний центр]] [[zh:活化位置]]