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"Stewart, Melissa"
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How does the ear hear? : and other questions about ... the five senses
\"What are the five senses? How do they help keep us safe? Why are two ears better than one? Why do some people need glasses? Why does food taste worse when we have a cold? And WHY can't we tickle ourselves? Find out in this SENSE-sational book!\"-- Provided by publisher.
Book
Biosensor reveals multiple sources for mitochondrial NAD
Nicotinamide adenine dinucleotide (NAD⁺) is an essential substrate for sirtuins and poly(adenosine diphosphate–ribose) polymerases (PARPs), which are NAD⁺-consuming enzymes localized in the nucleus, cytosol, and mitochondria. Fluctuations in NAD⁺ concentrations within these subcellular compartments are thought to regulate the activity of NAD⁺-consuming enzymes; however, the challenge in measuring compartmentalized NAD⁺ in cells has precluded direct evidence for this type of regulation. We describe the development of a genetically encoded fluorescent biosensor for directly monitoring free NAD⁺ concentrations in subcellular compartments. We found that the concentrations of free NAD⁺ in the nucleus, cytoplasm, and mitochondria approximate the Michaelis constants for sirtuins and PARPs in their respective compartments. Systematic depletion of enzymes that catalyze the final step of NAD⁺ biosynthesis revealed cell-specific mechanisms for maintaining mitochondrial NAD⁺ concentrations.
Journal Article
Monitoring glycolytic dynamics in single cells using a fluorescent biosensor for fructose 1,6-bisphosphate
Cellular metabolism is regulated over space and time to ensure that energy production is efficiently matched with consumption. Fluorescent biosensors are useful tools for studying metabolism as they enable real-time detection of metabolite abundance with singlecell resolution. For monitoring glycolysis, the intermediate fructose 1,6-bisphosphate (FBP) is a particularly informative signal as its concentration is strongly correlated with flux through the whole pathway. Using GFP insertion into the ligand-binding domain of the Bacillus subtilis transcriptional regulator CggR, we developed a fluorescent biosensor for FBP termed HYlight. We demonstrate that HYlight can reliably report the realtime dynamics of glycolysis in living cells and tissues, driven by various metabolic or pharmacological perturbations, alone or in combination with other physiologically relevant signals. Using this sensor, we uncovered previously unknown aspects of β-cell glycolytic heterogeneity and dynamics.
Journal Article
Deadliest animals
Young readers learn about 12 of the most deadly animals in the world, from sharks to tiny mosquitoes.
Book
Mechanisms of iron- and O2-sensing by the 4Fe-4S cluster of the global iron regulator RirA
RirA is a global regulator of iron homeostasis in Rhizobium and related α-proteobacteria. In its [4Fe-4S] cluster-bound form it represses iron uptake by binding to IRO Box sequences upstream of RirA-regulated genes. Under low iron and/or aerobic conditions, [4Fe-4S] RirA undergoes cluster conversion/degradation to apo-RirA, which can no longer bind IRO Box sequences. Here, we apply time-resolved mass spectrometry and electron paramagnetic resonance spectroscopy to determine how the RirA cluster senses iron and O2. The data indicate that the key iron-sensing step is the O2-independent, reversible dissociation of Fe2+ from [4Fe-4S]2+ to form [3Fe-4S]0. The dissociation constant for this process was determined as Kd = ~3 µM, which is consistent with the sensing of ‘free’ iron in the cytoplasm. O2-sensing occurs through enhanced cluster degradation under aerobic conditions, via O2-mediated oxidation of the [3Fe-4S]0 intermediate to form [3Fe-4S]1+. This work provides a detailed mechanistic/functional view of an iron-responsive regulator. Virtually all life forms require iron to survive, yet too much of the metal can be catastrophic. In healthy cells, many systems regulate this delicate balance. For instance, when a protein called RirA is active in Rhizobium bacteria, it can sense high levels of the metal and helps to shut down the production of proteins that bring in more iron. RirA contains a cluster of four iron and four sulphur atoms, which acts as a sensor for iron availability: however, exactly how this cluster structure detects the levels of the metal in a cell was previously unclear. Pellicer Martinez, Crack, Stewart et al. used a technique known as time-resolved mass spectrometry to examine the sensory response of the iron-sulphur cluster of RirA when different levels of iron were available. The results revealed a ‘loose’ iron atom in the cluster; when iron levels fall down, this atom is rapidly lost as it is scavenged for use in other essential processes. Without it, the cluster in RirA collapses and the protein becomes inactive. This prompts the cell to produce proteins that enable it to take up iron from its surroundings. Once iron levels are high, RirA can regain its cluster and is active again, stopping the production of proteins that bring in more iron. Iron-sulphur clusters are common in many proteins, and this work offers new insight into their various roles. It also highlights the potential to use time-resolved mass spectrometry to examine biological processes in depth.
Journal Article
Titanic
Discusses the Titanic, including its design, how the ship sank, the passengers onboard, and why the ship's legacy lives on.
Book
Evaluation of current feeding practices in the critically ill: A retrospective chart review
Worldwide, malnutrition is an important issue in the care of the critically ill which is associated with increased costs of care and poor patient outcomes.
To evaluate the current state of enteral nutrition in the critically ill in the U.S. in comparison to international practices.
A retrospective chart audit was performed utilising a 10% random sample of patients admitted to the Pulmonary Medicine Service at an academic medical center in the U.S. from 1/1/11 to 12/31/11. A total of 69 charts were audited.
Outcome measures included time to initiation of feeds, prescribed versus received protein and energy on day three, prokinetic use and markers of nutritional status.
Delayed time to feeding, greater than 48hours after ICU admission, was present in 66.7% of the sample. On day three only 9% of the sample was receiving 80% or more of the prescribed protein or energy. These findings are similar to those found internationally.
Critically ill patients continue to experience delays in enteral feeding initiation and are frequently not meeting nutrition targets. Interventions aimed at improving nutrition delivery in the intensive care unit should be a focus of quality care both in the U.S. and internationally.
Journal Article