Lock and key principle
The key-lock principle describes the function of two or more complementary structures that have to fit each other spatially in order to be able to fulfill a certain biochemical function. This principle was hypothetically described by Emil Fischer in 1894 using the example of the specific bond between enzyme and substrate . A weak, non- covalent interaction leads to a relatively stable transition state ( complex ) between ligand (guest) and receptor (host), the relative strength of which is called affinity . A somewhat more contemporary expression speaks of the induced-fit concept (hand-in-glove principle) in order to take into account the conformational flexibility of chemical compounds. Often it is only part of the overall structure of the ligand ( compare : pharmacophore ) or the receptor that is involved in the complex formation, the other part may remain functionally irrelevant.
- Biochemistry : Transmitters or modulators trigger biochemical processes at the receptor. B. drugs or drugs are exogenously simulated or antagonized.
- Endocrinology : The interaction between the mostly cell-based hormone receptors and hormones trigger corresponding signal chains that influence the function of the cell , as well as its differentiation.
- Enzymology : An enzyme facilitates a biochemical reaction by bringing the biogenic reactants together in a complex. Although the spatial structure of the substrate binding sites of the enzyme is genetically determined, the substrate binding can lead to comformative structural changes in the enzyme, which increase the catalytic effectiveness or make it possible in the first place.
- Immunology : The complex simultaneous interaction of several complementary structures at the interface of antigen- presenting and antigen-recognizing cells forms the prerequisite for specific antigen recognition (or more precisely, epitope recognition). For a more detailed description, see the antigen presentation .
The key-lock principle is also used in the following examples:
- All cells in cell aggregates ( tissue , organs ) have structures and complementary counter-structures on their cell surface, which are part of the communication between the cells and contribute to structural and functional cohesion.
- The prerequisite for antigen recognition is communication between the immune cells via complementary structures in order to differentiate between “self” and “foreign”.
- Immune cells that circulate in the body need surface structures in order to specifically “find” from place to place and back to their place of origin ( homing ).
- Sperm must find certain glycoproteins on the surface of the egg in order to enter it.
- Viruses require specific complementary structures (“docking sites”) in order to infect their host.
- Hermann J. Roth, Christa E. Müller, Gerd Folkers: Stereochemistry and Drugs, Wissenschaftliche Verlagsgesellschaft Stuttgart, 1998, pp. 251-274, ISBN 3-8047-1485-4 .