Influence of Krypton Gas Nanobubbles on the Activity of Pepsin

The fact that biologically inert gases can significantly affect the biological function of proteins still lacks a full understanding because they are usually chemically stable and weakly absorbed by biological molecules. Recently, nanobubbles were proposed to play an important role in the activity of a protein (Scientific reports 2013, 3; Scientific reports 2017, 7, 10176). In this study, we developed a controllable method to produce high-concentration krypton (Kr) gas nanobubbles in pure water and measured the concentration influence of those Kr nanobubbles on pepsin protein activity. By combining high-sensitivity synchrotron radiation X-ray fluorescence techniques with a nanoparticle tracking analysis technology, we provided strong evidence that the observed "nanoparticles" were indeed Kr nanobubbles. Activity measurements showed that the activity would be inhibited by the existence of Kr nanobubbles and could be recovered by degassing. More importantly, the inhibition extent of pepsin activity was dominated by the number of nanobubbles in solution. More nanobubbles would cause more inhibition of pepsin activity. Furthermore, the structures of pepsin could be changed by nanobubbles, which might be the reason for inhabitation of activity. Our results would provide a further understanding of the mechanisms of the biological effects of inert gases.