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Enzymes for Prodrug-Activation in Cancer Therapy
Published in Peter Grunwald, Pharmaceutical Biocatalysis, 2020
According to Siegel et al. (2018) the estimated number of new cases of malignant melanoma, a highly aggressive form of skin cancer, is 91,270 (55,150 males and 36,120 females) in the USA alone, with a death rate of 10%. Lowe et al. (2014) found that the incidence of cutaneous melanoma among middle-aged adults in the USA increased over the past 4 decades, which is in agreement with reports from other countries, but that disease-specific mortality has decreased, particularly in the last 10 years probably due among others to earlier detection through educational programs, and more skin cancer screenings. Melanoma is a complex and genomically diverse malignancy that has been reviewed by Lin and Fisher (2017) with respect to understanding of signaling and immune regulation in melanoma and implications for responses to treatment by multiple targeted therapies and immunotherapies that have meanwhile entered the clinic. This kind of cancer that in rare cases also occur in the mouth, intestines, or eye, develops from the melanin-containing so-called melanocytes; the skin pigment protects from UVB radiation (Riley, 2003). Among the different types of melanin the most common one is eumelanin with part of its structure shown in the scheme on the previous page; structural building blocks are among others 5,6-dihydroxyindole (DHI), 5,6-dihydroxyindole-2-carboxylic acid (DHICA), and L-dopamine; the arrows indicate possible sites of polymer growth. According to the Raper-Mason pathway (Mason, 1948) eumelanin formation results from the tyrosine hydroxylase and dopa oxidase activity of tyrosinase, an enzyme containing a pair of antiferromagnetically coupled copper ions in its active site. It is present in plant and animal tissues as well as in bacteria (e.g., Streptomyces sp.). The two Cu ions surrounded by six His residues bind one molecule of atmospheric oxygen, required for catalysis: the intermediate L-dopaquinone is formed during the reaction cycles to L-leukodopachrome and reacts with L-dopaquinone to L-dopachrome which is converted to the two eumelanin structural units DHI and DHICA. Further enzyme-catalyzed oxidation of these dihydroxyindoles gives indolequinones; polymer formation occurs via cross-linking reactions (Solano, 2014). A review of structure-function correlations in tyrosinases belonging to the type-3 copper protein family has been provided by Kanteev et al. (2015).
Green and efficient determination of ʟ-dopa in complex polypill formulations using a magnetic microplate
Published in Green Chemistry Letters and Reviews, 2018
Hweiyan Tsai, Chia-Yi Chen, Yi-Hsuan Lu, Ya-Yun Lai, Chwan-Bor Fuh
With this background in mind, we describe herein a high-throughput spectrophotometric method for the determination of ʟ-dopa in complex polypill formulations that overcomes these drawbacks. This assay is performed using reusable tyrosinase-immobilized magnetic nanoparticles (TYR-MNPs) and an in-house-prepared 96-well magnetic microplate, which provides a convenient system for the detection of multiple samples in a single run with low sample and reagent volumes. In our introduced system, detection is based on the tyrosinase-catalyzed oxidation of ʟ-dopa; we quantified ʟ-dopa by determining the absorption of dopachrome, the oxidation product of ʟ-dopa, at 475 nm. The reusability and stability of the TYR-MNPs were investigated, and two complex formulations, namely Madopar® and Stalevo®, were analyzed using this high-throughput spectrophotometric method.
Enzymatic biodegradation, kinetic study, and detoxification of Reactive Red-195 by Halomonas meridiana isolated from Marine Sediments of Andaman Sea, India
Published in Environmental Technology, 2023
Purbasha Saha, Sonal Madliya, Anmol Khare, Ikshita Subudhi, Kokati Venkata Bhaskara Rao
Tyrosinase: L-DOPA also known as l-3,4-dihydroxyphenylalanine was used as a substrate to measure tyrosinase activity. In the presence of tyrosinase activity, L-DOPA is converted to dopachrome. In this assay, 2.5 mM L-DOPA was added in 0.1 M phosphate buffer (pH 6.8). Reaction mixture was incubated at 37°C for 10 min, followed by the addition of the enzyme extract (0.1 mL). The assay was quantified by measuring a decrease in absorbance at 475 nm [30]. The activity of tyrosinase was calculated with the help of molar extinction co-efficient of dopachrome (ϵ = 3600/(M.cm)).