Tyrosinase (TYR) is a type III copper oxidase present in fungi, plants and animals. The inhibitor of human TYR plays a vital role in pharmaceutical and cosmetic fields by preventing synthesis of melanin in the skin. To search for an effective TYR inhibitor from various plant extracts, a kinetic study of TYR inhibition was performed with mushroom TYR. Among Panax ginseng, Alpinia galanga, Vitis vinifera and Moringa oleifera, the extracts of V. vinifera seed, A. galanga rhizome and M. oleifera leaf reversibly inhibited TYR diphenolase activity with IC₅₀ values of 94.8 ± 0.2 µg/mL, 105.4 ± 0.2 µg/mL and 121.3 ± 0.4 µg/mL, respectively. Under the same conditions, the IC₅₀ values of the representative TYR inhibitors of ascorbic acid and kojic acid were found at 235.7 ± 1.0 and 192.3 ± 0.4 µg/mL, respectively. An inhibition kinetics study demonstrated mixed-type inhibition of TYR diphenolase by A. galanga and V. vinifera, whereas a rare uncompetitive inhibition pattern was found from M. oleifera with an inhibition constant of K_ii 73 µg/mL. Phytochemical investigation by HPLC-MS proposed luteolin as a specific TYR diphenolase ES complex inhibitor, which was confirmed by the inhibition kinetics of luteolin. The results clearly showed that studying TYR inhibition kinetics with plant extract mixtures can be utilized for the screening of specific TYR inhibitors.

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Curcuma longa L., which belongs to the Zingiberaceae family, is a perennial herb distributed throughout tropical and subtropical regions of the world, being widely cultivated in Asiatic countries, Curcuminoids are inherent compounds of the species C. longa, there are three main compounds of this pigmented curcuminoid complex, namely, curcumin, demethoxycurcumin, and bisdemethoxycurcumin. Curcumin is the major component of this plant, being responsible for the activities. Crude extract of Curcuma longa rhizomes was prepared by using ethanol and Chemical detection was performed in order to investigate the secondary metabolites compounds of ethanolic crude extract. Reversed high performance liquid chromatography carried out for the detection and estimation of curcumin in the crude extract. Otherwise cytogenetic study of the effect of C. longa crude extract and standard curcumin on the normal human lymphocyte blood cells done after exposure to nickel chloride (NiCl2), furthermore, karyotyping was performed by using MetasystemIkaros. Chemical detection of crude extract showed positive result for alkaloids, tannins, glycosides, phenols, Terpens, flavonoids, cumarines and resins while showed negative result for Saponins and Steroids. While the results of the cytogenetic study revealed that the effect of C. longa crude extract and standard curcumin reduced the genotoxic effect of nickel chloride (NiCl2) on the normal human lymphocyte blood cells. Karyotyping showed that genotoxic effect of nickel chloride appeared as aberration in chromosome number 18. While lymphocytes treated with C. longa crude extract or standard curcumin showed no chromosomal aberration, at the same time no chromosomal aberration were observed after treatment with combination of NiCl2 and crude extract or combination of NiCl2 and standard curcumin which indicated the ability of standard curcumin and C. longa crude extract to prevent the effect of nickel chloride. Further medical cytogenetic and molecular testing to get better understanding the protective role of Curcuma longa rhizomes, crude extract against heavy metal induced chromosomal aberrations in human blood cultures.