Application Reagent for the irreversible inactivation of γ-cystathionase1,2; affinity labeling reagent for γ-cystathionase and other enzymes3; peptides containing this amino acid can be tritiated to high specific radioactivity4 Biochem/physiol Actions L-propargylglycine (PAG), an inhibitor of cystathionine γ-lyase (CSE), is useful in studies of hydrogen sulphide synthesis and bioactivity.