The Effect of Partially Reduced Graphene Oxide on The Enzymatic Activity of Yeast

Enzyme biocatalysts are important for the synthesis of drugs, vitamins, and other products, but research is being done to increase their stability and activity. Previously we have found that partially reduced graphene oxide (pRGO) acts as an enzymatic enhancer for the catalytic activity of microbial transglutaminase in the cross-linking of gelatin. We now set out to determine whether graphene oxide (GO) and/or pRGO would have an effect on the enzymatic activity of yeast to decompose hydrogen peroxide, thereby testing whether these 2D materials are biocompatible with a living organism that produces an enzymatic reaction rather than just testing the effect on the enzyme itself.<br/>A solution of pRGO reduced in a concentration of 18 mM sodium borohydride, as well as an unreduced GO solution, were compared with water as a control. While initial qualitative results suggested that GO had no effect on yeast’s catalytic activity, H2O2 decomposition seemed to be enhanced by 18 mm pRGO. However, further quantitative measurements were conducted by collecting O2 by water displacement. Twenty milligrams of yeast were suspended in two milliliters of water containing 0.2% sucrose by weight and incubated at 41 degrees Celsius for 4 minutes. (As a third variable, twenty milligrams of yeast were suspended in two milliliters of water containing 0.2% sucrose by weight but with 0.5 ml pRGO added to the yeast + water before incubation.) Then, 5 ml of 3% H2O2 + 0.5 ml DI water for the control, and 5 ml of 3% H2O2 + 0.5 ml pRGO for the test solution, were added and the time it took to displace 25 ml of water was measured. After 5 minutes, an additional 4 ml of 3% H2O2 were added, and the time it took to displace 25 ml water was again measured, to determine whether the yeast maintained its activity. Results showed that yeast activated in water had the same rate of decomposition of H2O2 containing pRGO as the control containing no pRGO, but yeast incubated in water containing pRGO actually had a slower rate of H2O2 decomposition, both initially as well as retesting five minutes later by adding additional H2O2. Macroscopic changes observed in the pRGO-yeast include darkening of the yeast, suggesting incorporation of pRGO by the cells. Microscopic examination of pRGO-incubated yeast at various time points provides further insight on the biocompatibility of partially reduced graphene oxide with living cells.