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Chemistry and Biochemistry of Vitamin C in Mammalian Systems
Published in Qi Chen, Margreet C.M. Vissers, Vitamin C, 2020
Margreet C.M. Vissers, Juliet M. Pullar, Nicholas Smirnoff
The breakdown of DHA to 2,3-DKG via hydrolysis not only results in the irreversible loss of ascorbate, it also introduces a plethora of metabolic possibilities due to the complex chemistry of 2,3-DKG breakdown (Figure 2.2). This topic was previously well reviewed [10,18,19,21,138] and is only summarized here. The 2,3-DKG readily breaks down, with decarboxylation generating L-xylonate and L-lyxonate [139]. This may be a less common reaction in mammalian systems, but if formed, these compounds can contribute to pentose phosphate pathways [10,19]. Alternatively, 2,3-DKG degradation can result in the production of L-erythrulose and oxalic acid [2,19,21], with potential metabolic consequences. The reactive compound L-erythulose can glycate proteins and cause protein cross-linking, and these reactions have been proposed to contribute to cataract formation in the lens of individuals with diabetes [140].
Histopathology
Published in Dimitris Rigopoulos, Alexander C. Katoulis, Hyperpigmentation, 2017
Self-tanners contain sugar molecules like dihydroxyacetone or erythrulose that react with proteins and amino acids of the cornified layer, leading to discoloration.4 The pigmentation can be seen as brownish discoloration of the uppermost corneocytes and in the form of pigmented droplets throughout the cornified layer (Figure 23.1).
Future Strategies for Commercial Biocatalysis
Published in Peter Grunwald, Pharmaceutical Biocatalysis, 2019
Robert E. Speight, Karen T. Robins
Szita and coworkers used two coupled microreactors in sequence to optimise the production of (2S,3R)-2-amino-1,3,4- butanetriol (Fig. 1.14; Gruber et al., 2018). Initially, the transketolase-catalysed asymmetric carbon-carbon bond formation, between hydroxypyruvate and glycoaldehyde to produce l-erythrulose, was optimised. The microreactor had a volume of 240 μl, which allowed rapid screening of the reaction conditions and enzyme concentration. Optimal conditions lead to complete conversion in 8 min at pH 7. The transaminase-catalysed amination of l-erythrulose, with methylbenzylamine as the amine donor, was optimised in a similar manner. The effect of each component from the preceding transketolase reaction mixture was also tested. It was discovered that the transketolase cofactor, thiamine pyrophosphate, inhibited the transaminase reaction. The optimised transaminase reaction required a reaction time of 2 h at pH 9. A coiled reactor was chosen to increase the retention time and the pH of the reaction mixture was adjusted before entering the second microreactor. When the two enzyme steps were coupled sequentially in the microreactors complete conversion occurred in just over 2 h. This was the first time that complete conversion for this reaction sequence had been reported. Coupled, two-step enzymatic cascade for the optimisation of (2S,3R)-2-amino-1,3,4-butanetriol synthesis in two sequentially coupled microreactors.Adapted from Gruber et al. (2018).
Metabolomics reveals the renoprotective effect of n-butanol extract and amygdalin extract from Amygdalus mongolica in rats with renal fibrosis
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2021
Wanfu Bai, Qing Liu, Hong Chang, Quanli Liu, Chen Gao, Yingchun Bai, Hongbing Zhou, Songli Shi
Among the 38 differentially expressed metabolites between the CON and MOD groups, 18 metabolites were acted on by either BUT or AMY, while 14 metabolites were co-acted on by BUT and AMY. Four metabolites were acted on by BUT alone. For example, diketogulonic acid (DKG) may be involved in damage to the kidney caused by oxalate. DKG is a vitamin C degradation metabolite. The vitamin C degradation pathway produces L-erythrulose and oxalate as final products, and the oxalate formed in this way may contribute to the formation of kidney stones in susceptible individuals [27]. AMY acted alone on four metabolites, which increased the excretion of toxic substances by increasing glucuronic acid conjugation. Glucuronidation assists the excretion of toxic substances, drugs, and other substances that cannot be used as an energy source.