Purification and characterisation of epithiospecifier protein from Brassica napus: enzymic intramolecular sulphur addition within alkenyl thiohydroximates derived from alkenyl glucosinolate hydrolysis

Epithiospecifier protein (ESP), a ferrous ion dependent protein, has a pote ntial role in regulating the release of elemental sulphur, nitriles, isothi ocyanates and cyanoepithioalkanes from glucosinolates, Two classes of ESP p olypeptides were purified with molecular masses of 39 and 35 kDa, and we sh ow that the previously reported instability was conditionally dependent. Th e 39 kDa polypeptide was made up of two distinct isozymes (5.00, 5.14) whil st several were present for the 35 kDa form of ESP (5.40-5.66). An anti-ESP antibody reacted with both the 39 and 35 kDa ESP forms in Brassica napus a nd strongly with a polypeptide corresponding to the 35 kDa ESP form in Cram be abyssinica, but did not detect any ESP in Sinapis alba or Raphanus sativ us, A cytochrome P-450 mediated iron dependent epoxidation tape mechanism i s suggested for ESP, (C) 2000 Federation of European Biochemical Societies.