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Components of Nutrition
Published in Christopher Cumo, Ancestral Diets and Nutrition, 2020
Glucose is one of several sugars available in foods. All cannot receive treatment here, but a handful has played important dietary and historical roles. Fructose, along with glucose, is the sugar in honey, high fructose corn syrup (HFCS), and many fruits and vegetables. Fructose has the same formula as glucose but a different structure and a unique metabolic pathway in the body. Chemists categorize the two as isomers because of these properties. Among natural sugars, fructose tastes sweetest. Sweetness is potent in HFCS, examined in Chapter 11, a product of corn starch. In the 1960s, American and Japanese chemists treated corn starch with enzymes to generate corn syrup. Addition of the enzyme xylose isomerase converted some of the resulting glucose into fructose such that HFCS is typically 45 percent glucose and 55 percent fructose, though the latter may be up to 90 percent.28 By comparison, sucrose, discussed below, is roughly half glucose and half fructose.
The Modification of Histidine Residues
Published in Roger L. Lundblad, Chemical Reagents for Protein Modification, 2020
A single histidine residue essential for catalysis by D-xylose isomerase has been identified by reaction with diethylpyrocarbonate.41 Instability of N-carboethoxyhistidine has made unequivocal identification of the histidyl residues modified by diethylpyrocarbonate difficult. In this study, the protein was first denatured in 6.0 M guanidine hydrochloride (pH 7.0) and then digested with subtilisin in 2.0 M guanidine hydrochloride at pH 7.0/30°C for 2 h. A single peptide containing the modified histidine residue was purified by HPLC using dual wavelength detection. In this technique, effluent is monitored by absorbance at 238 nm (the maximum in the difference spectrum between the modified and native protein) and absorbance at 214 nm (peptide bond absorbance). The ratio of A238/A214 was used to identify peptides containing the modified histidine residues.
Gut microbes and metabolites as modulators of blood-brain barrier integrity and brain health
Published in Gut Microbes, 2020
Aimée Parker, Sonia Fonseca, Simon R. Carding
Encouragingly, the ability to map connectivity between neurons manipulate neural activity in real time, and measure neural activity during behavior has produced a wealth of data approaching a “wiring diagram” of the bidirectional gut-brain control of appetite, able to describe and predict the effects of dietary nutrients, common hormones and regulators.94 Building on this, recent studies are attempting to connect altered bacterial metabolism to specific neural signaling affecting brain functions. For example, Schretter and colleagues114 describe how locomotor hyperactivity in germfree Drosophila (manifested as increased walking speed and daily activity) can be rescued by altering sugar metabolism, either by colonization with L. brevis or by administration of L. brevis-derived xylose isomerase. The behavioral hyperactivity effect in germfree flies was shown to be mediated by octapaminergic neurons, as specific stimulation of these neurons or exogenous administration of octopamine (the invertebrate counterpart of noradrenaline) prevented the rescue by xylose isomerase.114 In mouse models, in vivo cell-connectivity tracing and enteroendocrine-neural co-cultures have shown that glucose stimulation of CCK-positive enteroendocrine cells activates vagal nodose neurons by glutamate-based neurotransmission.99 What impact this signaling might have on regulation of BBB integrity and neurodegenerative disease remains to be determined, but it is an exciting step forward in connecting specific gut epithelial-neural circuits and developing the necessary understanding to trace microbe-to-brain communication.
Links between the gut microbiota, metabolism, and host behavior
Published in Gut Microbes, 2020
In our study, we found that specific bacteria modulate host locomotor behavior through changes in metabolism, and in neurotransmitters previously implicated in the regulation of host metabolism. We additionally discovered that a bacterial product involved in the interconversion of sugars, xylose isomerase, has similar effects on host behavior and related pathways. Given these connections, this work highlights the importance of examining microbial regulation of host metabolism in relation to its impact on host behavior.