4.2. Protein Tyrosine Phosphate 1B (PTP1B) Inhibitory Assay

PTP1B inhibitory activity was evaluated using pNPP [44]. Recombinant PTP1B enzyme (0.5 units diluted in PTP1B reaction buffer) was added to a plate with or without sample. The plate was pre-incubated at 37 °C for 10 min, and then substrate (2 mM pNPP) was added. Following incubation at 37 °C for 15 min, the enzymatic reaction was terminated by addition of 10 M NaOH. The absorbance was measured at 405 nm using a microplate spectrophotometer (Molecular Devices, Sunnyvale, CA, USA). Ursolic acid was used as a reference compound.