nerve growth factor

A peptide (13.26 kD) of 118 amino acids (usually dimeric) with both chemotropic and chemotrophic properties for sympathetic and sensory neurons. Found in a variety of peripheral tissues, NGF attracts neurites to the tissues by chemotropism, where they form synapses. The successful neurons are then "protected" from neuronal death by continuing supplies of NGF. It is also found at exceptionally high levels in snake venom and male mouse submaxillary salivary glands, from which it is commercially extracted. NGF was the first of a family of nerve tropic factors to be discovered. Amino acids 1-81 show homology with proinsulin. Besides its peripheral actions, NGF selectively enhances the growth of cholinergic neurons that project to the forebrain and that degenerate in Alzheimer\'s disease.