activators

An activator is a molecule that increases the activity of a protein, enzyme, or biological process. Activators work by promoting a more active conformation, stabilizing a functional complex, or enhancing the recruitment of other factors necessary for activity. They are distinct from inhibitors, which reduce activity, and from general cofactors that support catalysis without altering activity levels in a regulated sense.

Activators can be categorized by their mechanism and context. Allosteric activators bind sites separate from the active site and induce conformational changes that raise activity. Coactivators assist in transcription by enhancing the assembly or activity of the transcriptional machinery but may not bind DNA themselves. Covalent activators arise from signaling pathways that modify proteins, altering activity. Metal ions and small molecules can serve as essential or activating cofactors for certain enzymes.

Mechanisms of action vary across systems. In metabolism, activators such as AMP can increase enzyme activity by stabilizing the high-activity form or increasing substrate affinity; fructose-2,6-bisphosphate is an activator of PFK-1. In gene regulation, transcriptional activators bind to enhancer or promoter regions and recruit RNA polymerase through coactivator complexes; the bacterial CAP (catabolite activator protein) is activated by cAMP to promote transcription of specific genes. In eukaryotes, transcription factors like CREB require coactivators such as CBP/p300 to enhance transcription.

Applications and relevance include understanding metabolic control, signaling pathways, and drug design. Activators are used in research to modulate enzyme cascades or gene expression in engineered systems and to study regulatory networks in physiology.