Isolation and examination of thioglucoside glucohydrolase from seeds of Brassica napus

Thioglucoside glucohydrolase (EC 3.2.3.1) was extracted from seeds of Brassica napus cv. panter (rape) and purified by a procedure including gel filtration and ion exchange chromatography. Its specific activity using allylglucosinolate as substrate was more than twice that when using 2-hydroxybut-3-enylglucosinolate, even though the latter glucosinolate is the natural substrate in B. napus. At least two isoenzymes were detected with pH optima of 4.4 and 8.0. 5-Vinyloxazolidine-2-thione was the sole product of enzymic degradation of 2-hydroxybut-3-enylglucosinolate above pH 5.4 reaching a maximum at pH 8.0, whilst 1-cyano-2-hydroxybut-3-ene was the main product at low pH reaching a maximum at 3.4.