H-D-Phe-Pip-Arg-pNA (S-2238) dihydrochloride, a chromogenic substrate, is patterned after the N-terminal portion of the A alpha chain of fibrinogen, which is the natural substrate of thrombin. H-D-Phe-Pip-Arg-pNA dihydrochloride is specific for thrombin and is used to measure antithrombin-heparin cofactor (AT-III). The AT-III assay using H-D-Phe-Pip-Arg-pNA dihydrochloride is sensitive, accurate, and easy to perform.

PNPG is a chromogenic β-D-glucosidase substrate, producing a yellow solution upon cleavage.

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