Identification by shape-based virtual screening and evaluation of new tyrosinase inhibitors

Targeting tyrosinase is considered to be an effective way to control the production of melanin. Tyrosinase inhibitor is anticipated to provide new therapy to prevent skin pigmentation, melanoma and neurodegenerative diseases. Herein, we report our results in identifying new tyrosinase inhibitors. The shape-based virtual screening was performed to discover new tyrosinase inhibitors. Thirteen potential hits derived from virtual screening were tested by biological determinations. Compound 5186-0429 exhibited the most potent inhibitory activity. It dose-dependently inhibited the activity of tyrosinase, with the IC50 values 6.2 ± 2.0 µM and 10.3 ± 5.4 µM on tyrosine and L-Dopa formation, respectively. The kinetic study of 5186-0429 demonstrated that this compound acted as a competitive inhibitor. We believe the discoveries here could serve as a good starting point for further design of potent tyrosinase inhibitor.

Purification and characterization of 3,4-dihydroxyphenylalanine oxidative deaminase fromRhodobacter sphaeroidesOU5

An enzyme involved in the catabolism of 3,4-dihydroxyphenylalanine (DOPA) was isolated from Rhodobacter sphaeroides OU5. The enzyme catalyzes the formation of 3,4-dihydroxyphenylpyruvic acid (DOPP) and ammonia from DOPA. Formation of ammonia by DOPA oxidative deaminase was O2dependent and the enzyme isolated to its homogeneity has 100% affinity for DOPA. DOPA oxidative deaminase is functional at low concentrations of the substrate (<100 μmol·L–1) and is independent of NADH. The molecular mass of the purified enzyme is ~190 kDa and the enzyme could be a pentamer of 54, 42, 34, 25, and 23 kDa subunits as determined by SDS–PAGE.

Phenylalanine as substrate for tyrosine hydroxylase in bovine adrenal chromaffin cells

Incubation of bovine chromaffin cells with L-[14C]phenylalanine resulted in label accumulation in catecholamines at about 30% of the rate seen with L-tyrosine as precursor. Studies with purified tyrosine hydroxylase (EC 1.14.16.2) showed that the enzyme catalysed the hydroxylation of L-phenylalanine first to L-p-tyrosine and then to 3,4-dihydroxyphenylalanine (DOPA). No evidence for a significant involvement of an L-m-tyrosine intermediate in DOPA formation was found.