Editing Binding site (section)

=== Active site ===
{{Main|Active site}}
At the active site, a substrate binds to an enzyme to induce a chemical reaction.<ref name=":3">{{cite book | vauthors = Wilson K |chapter=Enzymes|date=March 2010|chapter-url=https://www.cambridge.org/core/books/principles-and-techniques-of-biochemistry-and-molecular-biology/enzymes/10382334B13C92480C86AA1E10F9DABD|pages=581–624|publisher=Cambridge University Press|language=en|doi=10.1017/cbo9780511841477.016|isbn=9780511841477|access-date=2018-11-01|title=Principles and Techniques of Biochemistry and Molecular Biology| veditors = Wilson K, Walker J }}</ref><ref>{{Cite book|title=Dictionary of Chemical Engineering| vauthors = Schaschke C |publisher=Oxford University Press|year=2014|isbn=978-1-62870-844-8}}</ref> Substrates, transition states, and products can bind to the active site, as well as any competitive inhibitors.<ref name=":3" /> For example, in the context of protein function, the binding of calcium to troponin in muscle cells can induce a conformational change in troponin. This allows for tropomyosin to expose the actin-myosin binding site to which the myosin head binds to form a [[Sliding filament theory|cross-bridge]] and induce a [[muscle contraction]].<ref>{{Cite book|title=Biology How Life Works| vauthors = Morris J | publisher= W.H. Freeman and Company|year=2016|isbn=978-1-4641-2609-3|location=United States of America|pages=787–792}}</ref>

In the context of the blood, an example of competitive binding is carbon monoxide which competes with oxygen for the active site on [[heme]]. Carbon monoxide's high affinity may outcompete oxygen in the presence of low oxygen concentration. In these circumstances, the binding of carbon monoxide induces a conformation change that discourages heme from binding to oxygen, resulting in carbon monoxide poisoning.<ref name="Hardin_2013" />
[[File:Enzyme inhibition.png|thumb|Competitive and noncompetitive enzyme binding at active and regulatory (allosteric) site respectively.]]