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The Sustainable Production of Polyhydroxyalkanoates from Crude Glycerol
Published in Martin Koller, The Handbook of Polyhydroxyalkanoates, 2020
Neha Rani Bhagat, Preeti Kumari, Arup Giri, Geeta Gahlawat
The first pathway for PHA synthesis from glycerol involves the combination of the glycolytic pathway and the TCA cycle. Here, glycerol is broken down into dihydroxyacetone (DHA) and glycerol-3-phosphate (G3P) with the help of the enzymes glycerol dehydrogenase (DhaD) and glycerol kinase (GlpK). These two molecules are then broken down into DHAP by the enzymes dihydroxyacetone kinase (DhaK) and glycerol 3-phosphate dehydrogenase [28]. This DHAP molecule is then converted into pyruvate via the glycolysis pathway. Furthermore, through the pyruvate dehydrogenase reaction, pyruvate is converted into acetyl-CoA in the presence of coenzyme A with the release of a CO2 molecule and reduction of NAD+ into NADH. Acetyl-CoA is the major intermediate molecule that further participates in the TCA cycle to form the next substrate, namely succinyl-CoA. Succinyl-CoA is then converted into succinate semialdehyde by the enzyme succinate semialdehyde dehydrogenase (SucD) [44]. Furthermore, succinate semialdehyde is converted into 4-hydroxybutyrate and 4-hydroxybutyryl-CoA via 4-hydroxybutyrate dehydrogenase (4hbD) and 4-hydroxybutyrate-CoA: CoA transferase (OrfZ) [44,45]. This formation of either HA-CoA or HB-CoA is considered as a major step in PHA synthesis where these end molecules get polymerized into scl-PHA molecules via PHA synthase enzymes.
Dihydroxyacetone levels in electronic cigarettes: Wick temperature and toxin formation
Published in Aerosol Science and Technology, 2018
Shawna Vreeke, Tetiana Korzun, Wentai Luo, R. Paul Jensen, David H. Peyton, Robert M. Strongin
Electronic cigarettes (e-cigarettes) have increased exponentially in popularity since their introduction a decade ago (Giovenco et al. 2015). Their usage among children and adolescents, which grew by 900% between 2011 and 2015, has been recognized as a major public health concern by the US Surgeon General (Murthy 2017). One in six US high school students currently uses e-cigarettes. In addition, the CDC reports that one in four middle school and high school students were exposed to secondhand e-cigarette aerosols (Wang et al. 2017b). Although the long-term health effects of e-cigarettes may not be known for many years, understanding the chemical profiles of their aerosols affords current insight into their potential toxicity. Recently, we identified 15 e-cigarette aerosol products formed upon aerosolization of the e-cigarette solvents propylene glycol (PG) and glycerol (GLY) (Jensen et al. 2017). Among these was dihydroxyacetone (DHA), the active ingredient in spray tanning products. Although DHA is approved by the FDA for external use in cosmetics, its use is restricted due to unknown inhalation risks (US FDA 2017). Research has shown that DHA can cause DNA damage (Peterson et al. 2004). DHA can be formed in e-cigarette aerosols via the free radical oxidation of glycerol followed by C-H cleavage (Scheme 1) (Fenton and Jackson 1899; Jensen et al. 2017). DHA is well-known to tautomerize to glyceraldehyde (Hall and Knowles 1975).