Catalyzes the conversion of methylthioalkyl glucosinolates of any chain length into methylsulfinylalkyl glucosinolates. a (Z)-omega-(methylsulfanyl)-N-sulfo-alkylhydroximate S-glucoside + H(+) + NADPH + O2 = a (Z)-omega-(methylsulfinyl)-alkyl-glucosinolate + H2O + NADP(+) Up-regulated in roots by salt, osmotic and cold stresses. No visible phenotype in leaves or seeds; due to the redundancy with other FMO GS-OXs. Belongs to the FMO family.