title: L-ascorbic acid 2-sulphate. A substrate for mammalian arylsulphatases.
abstract: Ascorbic acid 2-sulphate 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 mumol/mg per min (150 mumol/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 Km 12 21 mM ascorbic acid 2-sulphate. K2SO4 is a competitive inhibitor with a Ki 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 mumol/mg per min (90 mumol/mg per min for nitrocatechol sulphate at pH 5.6). In the absence of NaCl the activity is greatly decreased. Km is 8 mM. K2SO4 is a competitive inhibitor with a Ki 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.?
mesh_terms: D000818:Animals; D001192:Arylsulfatases / Q000378:metabolism*; D001205:Ascorbic Acid / Q000031:analogs & derivatives*; D001921:Brain / Q000201:enzymology; D002417:Cattle; D004355:Drug Stability; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008722:Methods; D009994:Osmolar Concentration; D012685:Sepharose; D013056:Spectrophotometry, Ultraviolet; D013429:Sulfatases / Q000378:metabolism*; D013464:Sulfuric Acids
chemical_list: D013464:Sulfuric Acids; D012685:Sepharose; D013429:Sulfatases; D001192:Arylsulfatases; D001205:Ascorbic Acid