RESUMO
Mushroom tyrosinase from Agaricus bisporus (abTYR) is often used during the development of tyrosinase inhibitors for medicinal and cosmetic purposes. In the search for novel tyrosinase inhibitors, this study identified hematoxylin as an alternative substrate for abTYR. The interaction of hematoxylin with abTYR was investigated through spectrophotometric and chromatographic analyses. The results showed that hematoxylin acted as an abTYR substrate and exhibited Michaelis-Menten kinetic behaviour at concentrations below 1.25 mM. The substrate properties of hematoxylin were similar to the natural tyrosinase substrate, L-3,4-dihydroxyphenylalanine (L-DOPA), with regards to Km, while Vmax was eightfold lower. The main oxidation product formed during the reaction of abTYR with hematoxylin was identified as hematein. This is the first report of the interaction of hematoxylin with abTYR.
RESUMO
Some Amaranthus species have been shown to have pharmacological properties such as activity against cancer, and it is also used as a traditional herbal medicine in many rural parts of the world. The (3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium bromide assay was used as a screening tool to determine the approximate cell viability inhibitory concentrations of methanol and aqueous crude extracts of Amaranthus spp. The extracts were screened using small-cell lung cancer (H69V), hepatocellular carcinoma (HepG2/C3A) and non-cancerous kidney cells (Vero) cell lines. Viability was assessed following exposure to a series of concentrations of each extract and A. hypochondriacus showed cytotoxicity of 70.55 µg/mL against H69V with a Si index of 1.8. The fractionated aqueous extract of 40 °C-treated A. hypochondriacus under well-watered conditions had a higher viability inhibition on H69V and Vero cell lines compared to the A. caudatus, A. cruentus and A. spinosus crude extracts. In conclusion, A. hypochondriacus could serve as a potential source of anticancer phytoconstituents for drug development.