"PGP9.5isasolublecytoplasmicproteinwithamolecularweightofapproximately25,000kD.Itispresentinneuronsandincellsofthediffuseneuroendocrinesystem.PGP9.5functionsasatissue-specificubiquitincarboxylterminalhydrolaseisoenzyme.ThisenzymeisalsoknownasUCH-L1.Becauseofitsabundanceinnerves,ithasbeenwidelyusedasaMarkerforperipheralnervefibers.ItwasalsodiscoveredasagenemutatedinsomerarefamialformsofParkinson"sdisease.InterestinglyacommonallelicvariantofUCHL1,theS18YpolymorphismisactuallyprotectiveagainstParkinson"sdisease.Itisalsoamarkerforcellsofthediffuseneuroendocrinesystemandtheirtumors"