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Naturally Occurring Polymers—Plants
Published in Charles E. Carraher, Carraher's Polymer Chemistry, 2017
UV radiation activates enzymes that modify the amino acid tyrosine in pigment-producing cells, the melanocytes. The enzyme tyrosinase, a copper-containing oxygenase, catalyzes the initial step, which is the hydroxylation of tyrosine to 3,4-dihydroxyphenylalanine that is oxidized to dopaquinone subsequently forming the melanins (Figure 9.12). The concentration of tyrosine is relatively high in skin protein. These modified tyrosine molecules undergo condensation, forming macromolecules known as melanins. Melanins have extended chain resonance where the pi electrons are associated with the growing melanin structure. As the melanin structure grows, it becomes more colored, giving various shades of brown color to our skin. This brown coloration acts to help protect the deeper skin elements from being damaged by the UV radiation. The absence of the enzyme tyrosinase that converts tyrosine to melanin can lead to albinism.
Bioactivities and phenolic composition of Limonium boitardii Maire and L. cercinense Brullo & Erben (Plumbaginaceae): two Tunisian strict endemic plants
Published in International Journal of Environmental Health Research, 2022
Ons Sefi, Soumaya Bourgou, Wided Megdiche-Ksouri, Mohamed Libiad, Abdelmajid Khabbach, Mohamed El Haissoufi, Fatima Lamchouri, Nikos Krigas, Zeineb Ghrabi-Gammar
Melanins, the main pigments primarily responsible in the skin and hair pigmentation, are produced by melanocytes through melanogenesis. Melanogenesis and skin pigmentation are the most important photoprotective factors in response to the damaging solar ultraviolet radiation inducing skin photocarcinogenesis. The increased melanin synthesis of these pigments occurs in many types of skin disorders, including Acanthosis nigricans, Cervical Poikiloderma, melasma, Periorbital hyperpigmentation, Lentigines and increased skin cancer risk. Tyrosinase enzyme possesses an essential role in the melanogenesis process since it catalyzes the hydroxylation of L-tyrosine to 3,4-dihydroxyphenylalanine (L-DOPA) and the oxidation of L-DOPA to dopaquinone. These reactions are considered rate-limiting steps for the melanin biosynthesis pathway, and therefore, for the production of skin pigments in melanocytes. Consequently, controlling the activity of this enzyme by tyrosinase inhibitors is an essential endeavor for treating pigmentary disorders in mammals. The mushroom tyrosinase inhibition biological assay is commonly used to investigate the whitening potential of natural extracts (Promden et al. 2018).
Extraction, anti-tyrosinase, and antioxidant activities of the collagen hydrolysate derived from Rhopilema hispidum
Published in Preparative Biochemistry & Biotechnology, 2021
Noor Atikah Ab Aziz, Norazlinaliza Salim, Mohammad Zarei, Nazamid Saari, Fatimah Md. Yusoff
These results were in agreement with the results obtained by Nakchum and Kim,[22] which showed the tyrosinase inhibition activity increased by increasing the concentration of collagen hydrolysate.[22] This is due to the use of protease enzyme or chemicals to hydrolyze protein into shorter length, which improve their functional properties.[26] Furthermore, the longer the time taken to hydrolyze the protein, the higher the amount of shorter peptide chains and free amino acids produced. Protein hydrolysate obtained from hydrolysis of chicken feather meal using papain showed that peptides with lower molecular weight (MW) exhibit higher inhibition of tyrosinase compared to peptides with higher MW.[15] Tyrosinase is an enzyme that promotes the pigmentation process by transforming the l-tyrosine to l-3,4-dihydroxyphenylalanine (l-DOPA) and the l-DOPA into dopaquinone, which further resulted in polymerization reaction of melanin production.[27] Therefore, tyrosinase inhibitor is a highly potential whitening agent as it hinders melanin production through inhibition of these enzymatic processes.[22]
Larvicidal and pathological effects of green synthesized silver nanoparticles from Artemisia herba-alba against Spodoptera littoralis through feeding and contact application
Published in Egyptian Journal of Basic and Applied Sciences, 2022
Raghda S. El-Ashmouny, Magda H. Rady, Bouthaina A. Merdan, T. A. A. El-Sheikh, Rasha E. Hassan, El Gohary E El Gohary
The detected morphological changes could be explained by the reduction in acetylcholine-choline esterase reaction, resulting in paralysis and knockdown of treated larvae. Destruction of the muscular system made larvae unable to take its normal C-shape (Figure 6). Demelanization (Figure 7 I.(b)) was due to the absence of copper tyrosinase, which convert tyrosine to dopaquinone forming melanin pigment. Competition between Ag and Cu ions made Ag ions to replace copper leading to Cu2+ starvation resulting in demelanization [67].