Specifically, acetylation refers to the process of introducing an acetyl group (resulting in an acetoxy group) into a compound, namely, the substitution of an acetyl group for an active hydrogen atom. A reaction involving the replacement of the hydrogen atom of a hydroxyl group with an acetyl group (CH3 CO) yields a specific ester, the acetate. Acetic anhydride is commonly used as an acetylating agent reacting with free hydroxyl groups. For example, it is used in the synthesis of aspirin and heroin.
Acetylation of proteins
Acetylation is important in cell biology because acetyl groups can turn proteins and genes on and off.
Acetylation occurs as a co-translational and post-translational modification of proteins, for example, histones, p53, and tubulins. In fact, proteomics studies have identified thousands of acetylated mammalian proteins. Among these proteins, chromatin proteins and metabolic enzymes are highly represented, indicating that acetylation has a considerable impact on gene expression and metabolism. In bacteria, 90% of proteins involved in central metabolism of Salmonella enterica are acetylated.
Acetylation of the amino terminus occurs in about 50% of yeast proteins and more than 80% of human proteins. The reaction is catalyzed by N-terminal acetyltransferases, occurs predominantly during protein synthesis and appears to be irreversible. Acetylation of the amino terminus of a protein can function as degradation signal (degron).
Lysine acetylation and deacetylation
Proteins are typically acetylated on lysine residues and this reaction relies on acetyl-coenzyme A as the acetyl group donor. In histone acetylation and deacetylation, histone proteins are acetylated and deacetylated on lysine residues in the N-terminal tail as part of gene regulation. Typically, these reactions are catalyzed by enzymes with histone acetyltransferase (HAT) or histone deacetylase (HDAC) activity, although HATs and HDACs can modify the acetylation status of non-histone proteins as well.
The regulation of transcription factors, effector proteins, molecular chaperones, and cytoskeletal proteins by acetylation and deacetylation is a significant post-translational regulatory mechanism  These regulatory mechanisms are analogous to phosphorylation and dephosphorylation by the action of kinases and phosphatases. Not only can the acetylation state of a protein modify its activity, there has been recent suggestion that this post-translational modification may also crosstalk with phosphorylation, methylation, ubiquitination, sumoylation, and others for dynamic control of cellular signaling.
The regulation of tubulin protein is an example of this in mouse neurons and astroglia. A tubulin acetyltransferase is located in the axoneme, and acetylates the α-tubulin subunit in an assembled microtubule. Once disassembled, this acetylation is removed by another specific deacetylase in the cell cytosol. Thus axonemal microtubules, which have a long half-life, carry a "signature acetylation" which is absent from cytosolic microtubules which have a shorter half-life.
Acetylation of wood
Since the beginning of the 20th century, acetylation of wood was researched as a method to upgrade the durability of wood in resistance against rotting processes and molds. Secondary benefits is the improvement of dimensional stability, improved surface hardness and no decrease in mechanical properties due to the treatment. The physical properties of any material are determined by its chemical structure. Wood contains an abundance of chemical groups called “free hydroxyls”. Free hydroxyl groups adsorb and release water according to changes in the climatic conditions to which the wood is exposed. This is the main reason why wood swells and shrinks. It is also believed that the digestion of wood by enzymes initiates at the free hydroxyl sites – which is one of the principal reasons why wood is prone to decay.
Acetylation effectively changes the free hydroxyls within the wood into acetyl groups. This is done by reacting the wood with acetic anhydride, which comes from acetic acid (known as vinegar when in its dilute form). When the free hydroxyl group is transformed to an acetyl group, the ability of the wood to absorb water is greatly reduced, rendering the wood more dimensionally stable and, because it is no longer digestible, extremely durable.
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