Timothy
Chen
Sponsor: Michael Toney, Ph.D. Chemistry Pyridoxal 5'-phosphate (PLP)-dependent enzymes represent about 4% of all known enzyme activities. PLP-dependent aspartate aminotransferase (AAT) was previously found to exhibit enhanced catalytic activity with L-Asp upon exposure to blue light. The light enhancement is attributed to the photoinduced deprotonation of Cα-H on the external aldimine intermediate to form the quinonoid intermediate, a partially rate-limiting step in the enzymatic catalysis. This project attempts to understand how general this phenomenon of light-enhanced catalysis is with other PLP-dependent enzymes and their reactions, since they share the similar chemistry. The five enzymatic reactions being explored include AAT with cysteine sulfinate, dialkylglycine decarboxylase (DGD) with aminoisobutyric acid (AIB), DGD with L-Ala, wild-type alanine racemase (AR) with D-Ala, and R219E AR with D-Ala. Steady-state kinetics and stopped-flow kinetics are used to observe catalytic activity increases after exposure to blue light. With the generalization of this light-enhanced kinetics, the conclusion may impact enzyme kinetics in plant biochemistry, animal biochemistry, human medicine, pharmacology, and many related applied fields due to the abundance of PLP-dependent enzymes in nature. Influence of Nitrogen Availability on Early Development in a Native and Invasive Forb
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Timothy Chen
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Nitrogen, an essential plant nutrient, is important in grassland competition dynamics. Nitrogen-based fertilizers are commonly applied, though most of the current literature on grassland species focuses on community effects of nitrogen, which leaves out the detailed morphological effects of both nitrogen addition and removal in stages of early growth. I compared the effect of nitrogen addition and limitation on the above and below ground traits of California native, Hemizonia congesta (hayfield tarweed), and its non-native counterpart, Centaurea solstitialis (yellow starthistle). This study involves observing germination and trait development for 10 weeks, using trait differences as proxies for fitness. I predict C. solstitialis will have greater biomass, height, and leaf area under the high nitrogen treatment, but that H. congesta will exhibit faster and more expansive root growth in the low nitrogen treatment. This study will shed light on how native and invasive species respond to varying nitrogen availability, informing nitrogen's role in early plant establishment in California grasslands. For grassland managers, trait differences in response to nitrogen availability could inform timing decisions of when to apply or immobilize nitrogen, utilizing it as a tool to limit the spread of C. solstitialis or promote the growth of natives such as H. congesta. UC Davis 34 th Annual Undergraduate Research, Scholarship and Creative Activities Conference 55 Seasonal Dynamics of Methane Emissions and Their Microbial Controls in the Amazon Rainforest Grace Cheng
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UC Davis / Plant Sciences / 2023
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Timothy Chen