Class I, II and IV are considered "classical" HDACs whose activities are inhibited by trichostatin A (TSA) and have a zinc dependent active site, whereas Class III enzymes are a family of NAD+-dependent proteins known as sirtuins and are not affected by TSA.

HDAC6 deacetylates tubulin, Hsp90, and cortactin, and forms complexes with other partner proteins, and is, therefore, involved in a variety of biological processes.

[16] Histone tails are normally positively charged due to amine groups present on their lysine and arginine amino acids.

It is a mistake to regard HDACs solely in the context of regulating gene transcription by modifying histones and chromatin structure, although that appears to be the predominant function.

The acetylation of lysine residues is emerging as an analogous mechanism, in which non-histone proteins are acted on by acetylases and deacetylases.

Histone deacetylase inhibitors (HDIs) have a long history of use in psychiatry and neurology as mood stabilizers and anti-epileptics, for example, valproic acid.

[32] In addition, a clinical trial is studying valproic acid effects on the latent pools of HIV in infected persons.

[33] HDIs are currently being investigated as chemosensitizers for cytotoxic chemotherapy or radiation therapy, or in association with DNA methylation inhibitors based on in vitro synergy.

HDIs have been shown to alter the activity of many transcription factors, including ACTR, cMyb, E2F1, EKLF, FEN 1, GATA, HNF-4, HSP90, Ku70, NFκB, PCNA, p53, RB, Runx, SF1 Sp3, STAT, TFIIE, TCF, and YY1.

[38][39] The ketone body β-hydroxybutyrate has been shown in mice to increase gene expression of FOXO3a by histone deacetylase inhibition.

Histone deacetylase inhibitors have shown activity against certain Plasmodium species and stages which may indicate they have potential in malaria treatment.