Catalyzes the conversion of methylthioalkyl glucosinolates into methylsulfinylalkyl glucosinolates. Able to S-oxygenate both desulfo- and intact 4-methylthiobutyl glucosinolates, but no activity with methionine, dihomomethionine or 5-methylthiopentaldoxime. a (Z)-omega-(methylsulfanyl)-N-sulfo-alkylhydroximate S-glucoside + H(+) + NADPH + O2 = a (Z)-omega-(methylsulfinyl)-alkyl-glucosinolate + H2O + NADP(+) Mainly expressed in leaves. Low levels in flowers and seeds. Increased accumulation of methylthiobutyl, -pentyl and -heptyl glucosinolates in leaves. No effects in seeds. Belongs to the FMO family.