(S)-2-hydroxypropylphosphonic acid epoxidase (, HPP epoxidase, HppE, 2-hydroxypropylphosphonic acid epoxidase, Fom4, (S)-2-hydroxypropylphosphonate epoxidase) is an enzyme with systematic name (S)-2-hydroxypropylphosphonate,NADH:oxygen epoxidase. This enzyme catalyses the following chemical reaction
(S)-2-hydroxypropylphosphonic acid epoxidase contains one non-heme iron centre per monomer. The product is the antibiotic fosfomycin.