Either monoamine oxidase A (MAO) or catechol-O-methyltransferase (COMT) can catalyze the first step in catecholamine catabolism. The potentially toxic aldehyde intermediate generated in the MAO reaction (3,4-dihydroxyphenylacetaldehyde for dopamine, 3,4-dihydroxyphenylglycolaldehyde for norepinephrine) is either rapidly reduced to an alcohol (by
The search for a functional thrombin receptor, using expression cloning methods, led to the discovery of a G protein-coupled receptor that mediates the actions of thrombin on platelets and endothelial cells.
Neurotensin is a 13 amino acid regulatory peptide found mainly in gut and brain. Intestinal neurotensin is produced by a discrete population of endocrine cells (N cells) scattered throughout the jejuno-ileal mucosa.
Heterotrimeric G proteins, comprising α, β and γ subunits, respond to extracellular signals generated by activated seven-transmembrane (7TM) receptors by modulating intracellular effector proteins such as enzymes and ion channels.