Initial and Final Products, Nitriles, and Ascorbigens Produced in Myrosinase-Catalyzed Hydrolysis of Indole Glucosinolates

Abstract

Micellar electrokinetic capillary chromatography (MECC) was used to follow the myrosinase (β-thioglucoside glucohydrolase EC 3.2.3.1)-catalyzed transformation of glucobrassicin (indol-3-ylmethylglucosinolate, 1a) and neoglucobrassicin (N-methoxyglucobrassicin, 1b) into nitriles, ascorbigens, and other products. The influence of pH, ascorbic acid, and Fe(II) ions was investigated. In the presence of ascorbic acid, (5 mM), thiocyanate ion and ascorbigens were the dominating products from 1a and 1b. In the presence of Fe(II) ions (2.5 mM), nitriles were the dominating products between pH 4 and 6−7. During hydrolysis of 1b in neutral or weakly basic solution, an unstable intermediate was detected by MECC. Comparisons of the rate of ascorbigen formation from 1a, 1b, and indol-3-ylcarbinol showed that ascorbigens were formed directly from ascorbate and unstable products of the hydrolysis of indole glucosinolates and that indol-3-ylcarbinols were not important intermediates. Structures of 1a, 1b, and products of 1b were confirmed by 1H NMR, MS, and UV spectroscopy. Keywords: Indole glucosinolate; myrosinase; ascorbigen; isothiocyanate; nitrile