Editing Active site (section)

===Lock and key hypothesis===

This concept was suggested by the 19th-century chemist [[Hermann Emil Fischer|Emil Fischer]]. He proposed that the active site and substrate are two stable structures that fit perfectly without any further modification, just like a key fits into a lock. If one substrate perfectly binds to its active site, the interactions between them will be strongest, resulting in high catalytic efficiency.

As time went by, limitations of this model started to appear. For example, the competitive [[enzyme inhibitor]] [[methylglucoside]] can bind tightly to the active site of [[4-alpha-glucanotransferase]] and perfectly fits into it. However, 4-alpha-glucanotransferase is not active on methylglucoside and no glycosyl transfer occurs. The Lock and Key hypothesis cannot explain this, as it would predict a high efficiency of methylglucoside glycosyl transfer due to its tight binding. Apart from competitive inhibition, this theory cannot explain the mechanism of action of [[Non-competitive inhibition|non-competitive inhibitors]] either, as they do not bind to the active site but nevertheless influence catalytic activity.<ref name="Daniel">{{cite journal|vauthors=Daniel E|date=1995|title=The Key–Lock Theory and the Induced Fit Theory|journal=[[Angewandte Chemie International Edition]]|volume=33|issue=2324|pages=2375–2378|doi=10.1002/anie.199423751}}</ref>