PYR test determines the activity of enzyme L-pyrroglutamyl amino-peptidase produced by Streptococcus pyogenes but not by other beta hemolytic Streptococci. L-pyrrolidonyl-β-naphthylamide (PYR) serves as a substrate for the detection of L-pyrroglutamyl amino-peptidase. The enzyme peptidase hydrolyzes the substrate PYR to produce β-naphthylamide. β-naphthylamide is detected in the presence of N, N-dimethylaminocinnamaldehyde reagent by the production of bright red-colored product.