ISSN:
1471-4159
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
Approximately 80 per cent of tyrosine hydroxylase activity in bovine mandibular nerve and rabbit sciatic nerve was soluble, and the rest of the activity was particle-bound. The soluble enzyme in bovine mandibular nerve was isolated by ammonium sulphate fractionation (25–35 per cent saturation). The enzyme had a pH optimum at 5·9 in Tris-acetate buffer, and at 6·5 in Tris-HCl or phosphate buffer. The enzyme required a tetrahydropteridine cofactor. Km values toward various tetrahydropteridines such as l-erythro-tetrahydrobiopterin (a probable natural cofactor), 2-amino-4-hydroxy-6-methyltetrahydropteridine, and 2-amino-4-hydroxy-6,7-dimethyltetrahydropteridine were 2 × 10−5m, 5 × 10−5m and 4 × 10−4m, respectively. The Km value for tyrosine at 1 × 10−3m-2-amino-4-hydroxy-6-methyltetrahydropteridine as a cofactor was 5 × 10−5m. The enzyme activity was markedly stimulated with Fe2+ or catalase, but Fe2+ gave higher activity. The activity was inhibited with α, α′-dipyridyl, l-α-methyl-p-tyrosine, and various catecholamines. Among catecholamines, dopamine was the most potent inhibitor. l-5-Hydroxytryptophan was an inhibitor as potent as dopamine. Neither d-5-hydroxytryptophan nor 5-hydroxytryptamine inhibited the enzyme. The inhibition by l-5-hydroxytryptophan was partially competitive with tetrahydrobiopterin at concentrations higher than 9 × 10−5m, and partially uncompetitive at concentrations lower than 9 × 10−5m. The addition of heparin or lysolecithin did not affect enzyme activity with tetrahydrobiopterin as cofactor.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1471-4159.1975.tb11882.x
Permalink
