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Browsing by Author "You, Chun"

Now showing 1 - 3 of 3
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    A high-energy-density sugar biobattery based on a synthetic enzymatic pathway
    Zhu, Zhiguang; Tam, Tsz Kin; Sun, Fangfang; You, Chun; Zhang, Y. H. Percival (Springer Nature, 2014-01)
    High-energy-density, green, safe batteries are highly desirable for meeting the rapidly growing needs of portable electronics. The incomplete oxidation of sugars mediated by one or a few enzymes in enzymatic fuel cells suffers from low energy densities and slow reaction rates. Here we show that nearly 24 electrons per glucose unit of maltodextrin can be produced through a synthetic catabolic pathway that comprises 13 enzymes in an air-breathing enzymatic fuel cell. This enzymatic fuel cell is based on non-immobilized enzymes that exhibit a maximum power output of 0.8 mW cm(-2) and a maximum current density of 6 mA cm(-2), which are far higher than the values for systems based on immobilized enzymes. Enzymatic fuel cells containing a 15% (wt/v) maltodextrin solution have an energy-storage density of 596 Ah kg(-1), which is one order of magnitude higher than that of lithium-ion batteries. Sugar-powered biobatteries could serve as next-generation green power sources, particularly for portable electronics.
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    New insights into enzymatic hydrolysis of heterogeneous cellulose by using carbohydrate-binding module 3 containing GFP and carbohydrate-binding module 17 containing CFP
    Gao, Shuhong; You, Chun; Renneckar, Scott; Bao, Jie; Zhang, Yi-Heng P. (2014-02-19)
    Background The in-depth understanding of the enzymatic hydrolysis of cellulose with heterogeneous morphology (that is, crystalline versus amorphous) may help develop better cellulase cocktail mixtures and biomass pretreatment, wherein cost-effective release of soluble sugars from solid cellulosic materials remains the largest obstacle to the economic viability of second generation biorefineries. Results In addition to the previously developed non-hydrolytic fusion protein, GC3, containing a green fluorescent protein (GFP) and a family 3 carbohydrate-binding module (CBM3) that can bind both surfaces of amorphous and crystalline celluloses, we developed a new protein probe, CC17, which contained a mono-cherry fluorescent protein (CFP) and a family 17 carbohydrate-binding module (CBM17) that can bind only amorphous cellulose surfaces. Via these two probes, the surface accessibilities of amorphous and crystalline celluloses were determined quantitatively. Our results for the enzymatic hydrolysis of microcrystalline cellulose (Avicel) suggested that: 1) easily accessible amorphous cellulose on the surface of Avicel is preferentially hydrolyzed at the very early period of hydrolysis (that is, several minutes with a cellulose conversion of 2.8%); 2) further hydrolysis of Avicel is a typical layer-by-layer mechanism, that is, amorphous and crystalline cellulose regions were hydrolyzed simultaneously; and 3) most amorphous cellulose within the interior of the Avicel particles cannot be accessed by cellulase. Conclusions The crystallinity index (CrI), reflecting a mass-average (three-dimensional) cellulose characteristic, did not represent the key substrate surface (two-dimensional) characteristic related to enzymatic hydrolysis.
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    Recyclable Cellulose-Containing Magnetic Nanoparticles: Immobilization of Cellulose-Binding Module-Tagged Proteins and Synthetic Metabolon Featuring Substrate Channeling
    Myung, Suwan; You, Chun; Zhang, Y. H. Percival (The Royal Society of Chemistry, 2013-07-01)
    Easily recyclable cellulose-containing magnetic nanoparticles were developed for immobilizing family 3 cellulose-binding module (CBM)-tagged enzymes/proteins and a self-assembled three-enzyme complex called the synthetic metabolon. Avicel (microcrystalline cellulose)-containing magnetic nanoparticles (A-MNPs) and two controls of dextran-containing magnetic nanoparticles (D-MNPs) and magnetic nanoparticles (MNPs) were prepared by a solvothermal method. Their adsorption ability was investigated by using CBM-tagged green fluorescence protein and phosphoglucose isomerase. A-MNPs had higher adsorption capacity and tighter binding on CBM-tagged proteins than the two control MNPs because of the high-affinity adsorption of CBM on cellulose. In addition, A-MNPs were used to purify and co-immobilize a three-enzyme metabolon through a CBM-tagged scaffoldin containing three different cohesins. The three-enzyme metabolon comprised of dockerin-containing triosephosphate isomerase, aldolase, and fructose 1,6-bisphosphatase was self-assembled because of the high-affinity interaction between cohesins and dockerins. Thanks to spatial organization of the three-enzyme metabolon on the surface of A-MNPs, the metabolon exhibited a 4.6 times higher initial reaction rate than the non-complexed three-enzyme mixture at the same enzyme loading. These results suggested that the cellulose-containing MNPs were new supports for immobilizing enzymes, which could be selectively recycled or removed from other biocatalysts by a magnetic force, and the use of enzymes immobilized on A-MNPs could be very useful to control the On/Off process in enzymatic cascade reactions.