Substrate Peptides

An enzyme substrate is a molecule upon which an enzyme acts. In the case of a single substrate, the substrate binds to the enzyme active site, and an enzyme-substrate complex is formed. The substrate is then transformed into one or more products which are then released from the active site. The discovery of substrates for enzymes with exclusive, selective activities is a central goal in biochemistry and an enzyme assay that measures catalytic function can be a valuable tool for drug discovery, used to identify inhibitors, estimate affinity, characterize molecular mechanisms of action and evaluate selectivity. Establishing an enzyme assay requires identification of a suitable substrate and the sensitivity and specificity of synthetic peptide substrates has made them the substrate of choice in many settings.
Substrate peptides are particularly useful in kinase assays. Kinases modulate a wide variety of cellular events, including differentiation, proliferation, metabolism and apoptosis. The substrates for kinases vary from large proteins to small peptides to sugars and lipids. Substrate screening is the first step in the fundamental investigation of protein kinases.
A substrate is called chromogenic if it gives rise to a coloured product when acted on by an enzyme. Similarly if it gives rise to a fluorescent product it is called a fluorogenic substrate.

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