l-ascorbic acid 2-sulphate
| Autor: | A.B. Roy |
|---|---|
| Rok vydání: | 1975 |
| Předmět: | |
| Zdroj: | Biochimica et Biophysica Acta (BBA) - Enzymology. 377:356-363 |
| ISSN: | 0005-2744 |
| DOI: | 10.1016/0005-2744(75)90316-2 |
| Popis: | Ascorbic acid 2-sulphage has a stability in acid comparable to that of phenyl sulphate and is rather more acid-labile than simple carbohydrate sulphates. At its optimum pH of 4.8 sulphatase A(aryl-sulphate sulphohydrolase EC 3.1.6.1.) hydrolyses ascorbic acid sulphate with a specific activity of 90 μmol/mg per min (150 μmol/mg per min with nitrocatechol sulphate at pH 5.6). At pH 4.8 the kinetics are non-Michaelis. At pH 5.6 Michaelis kinetics are obeyed and K m is 21 mM ascorbic acid 2-sulphate. K 2 SO 4 is a competitive inhibitor with a K i of 0.2 and 0.6 mM at pH 4.8 and 5.6, respectively. Sulphatase A is converted into a substrate-modified form during its hydrolysis of ascorbic acid sulphate. Sulphatase B also hydrolyses ascorbic acid 2-sulphate. At pH 4.8 and in the presence of 0.15 M NaCl the specific activity is 0.92 μmol/mg per min (90 μmol/mg per min for nitrocatechol sulphate at pH 5.6). In the absence of NaCl the activity is greatly decreased. K m is 8 mM. K 2 SO 4 is a competitive inhibitor with a K i of 0.1 mM. Ascorbic acid is not hydrolysed at a detectable rate by the arylsulphatases of the mollusc Dicathais orbita or of Aerobacter aerogenes . |
| Databáze: | OpenAIRE |
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