The Effects of Graphene Oxide and Partially Reduced Graphene Oxide on the Enzymatic Activity of Microbial Transglutamina
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.89
The Effects of Graphene Oxide and Partially Reduced Graphene Oxide on the Enzymatic Activity of Microbial Transglutaminase in Gelatin Rebecca Isseroff; Jerry Reyes; Roshan Reddy; Nicholas Williams; Miriam Rafailovich Stony Brook University, Stony Brook, NY
ABSTRACT A significant drawback of enzyme use in industrial applications is its lack of stability. Graphene oxide (GO) has previously been investigated for enzyme immobilization and enhancement of enzymatic catalysis. Microbial transglutaminase (MTG) is an enzyme that is used to modify food proteins, increase durability of textiles, and crosslink hydrogels for drug delivery. We tested the effects of adding GO and partially reduced GO (pRGO) to water solutions of gelatin and then crosslinking it with MTG, measuring both the resulting gelatin modulus and then the time it took for the onset of gelation. We found that the presence of pRGO in a gelatin-MTG-water mixture (when using 0.75 g MTG in 10 ml of gelatin solution) significantly increases the modulus by 60% more than the control. Using this same concentration of MTG, we measured the onset of gelation time and found that pRGO in gelatin solution reduces the onset of gelation time by nearly 50% while inducing a very large increase in viscosity by three orders of magnitude, whereas the addition of GO increases the onset of gelation time by 33% and decreases the viscosity of the gel by more than one order of magnitude. The very large enhancement by pRGO of the viscosity may be due to pRGO’s electron withdrawing ability and/or may also be due to adsorption of gelatin to the pRGO platelets which effectively increases the crosslinking density through non-enzymatic processes assisting the enzymatic activity.
INTRODUCTION Enzyme biocatalysis has become important on an industrial level for the synthesis of drugs, vitamins, and other products. However, enzyme use has its drawbacks; enzymes undergo denaturation, and they can become unstable under
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industrial operating conditions or during long storage [1]. To solve this problem, many have increased the stability of the enzymes by immobilizing them on graphene oxide [2]. Graphene oxide (GO) is composed of sheets of carbon atoms containing oxygen, carboxyl and hydroxyl functional groups, so it is water-soluble and has a high surface area. It has been hypothesized that GO can form hydrogen bonds with other biomolecules, enabling GO to react in a different manner than other 2D materials such as graphene and boron nitride which do not have these functional groups [3]. For example, lipase hydrolysis activity increased by 55% when the enzyme was immobilized on GO [2]. Trypsin activity for casein digestion was enhanced by GO nanosheets coated with polyethylene gl
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