## 2 Materials and Methods
### AFM Experiments and Sample Preparation  
The experiments were carried out by the direct surface adsorption method [45]. In this method, the protein objects to be studied adsorb onto the AFM substrate surface during its incubation in the analyzed solution. Herein, mica sheets (SPI, West Chester, PA, USA) were employed as AFM substrates with a hydrophilic surface. The samples for the AFM measurements were prepared as follows. A \(7\times 15\) mm piece of mica sheet was immersed into 800 uL of the analyzed 0.1 uM (\(10^{-7}\) M) HRP solution in 2 mM potassium phosphate buffer (pH 7.4), which was either exposed (working experiment) or not exposed to the field (control experiment). The mica substrate was incubated in the analyzed solution for 10 min in a shaker (Thermomixer Comfort, Eppendorf, Germany) at 600 rpm and room temperature. After the incubation, each substrate was first rinsed with the ultrapure distilled water and then scanned by AFM in air at 60% air humidity. Under such conditions, biological macromolecules were reported to retain their native structure owing to the presence of a water layer on the surface of bare mica [62]. Figure 2: Schematic representation of an ISTRA conventional shock tube experimental setup. Numbers indicate the main elements of the setup: 1 is the high-pressure chamber; 2 is the destructible copper membrane; 3 is the low-pressure chamber; 4 is the measuring section of the low-pressure chamber containing pressure sensors; 5 is the sample with a test tube containing a solution of HRP enzyme placed at the end of the shock tube. The protein concentration used in the experiments was dictated by inherent limitations of the AFM-based technique: at higher concentrations the molecules under study formed continuous layers on the mica substrate, making the identification of individual objects impossible. It should be emphasized that the concentration studied is still relevant physiologically: the concentration of glutathione peroxidase in human plasma was reported to be \(\sim\)10\({}^{-7}\) M [10]. The mica substrate surface with adsorbed HRP was visualized by AFM. AFM allows one to measure the heights of the visualized biological macromolecules with high (down to 0.1 nm) resolution [42; 43]. At the same time, the lateral dimensions of the AFM images of the visualized objects can be broadened due to the effect of convolution of the probe and the objects under study, as the AFM tip has a certain curvature radius [63]. For this reason, herein, the height of AFM images was used as a criterion for the estimation of a change in the size of the visualized objects. All AFM experiments were performed in tapping mode with a Titanium multimode atomic force microscope (NT-MDT, Moscow, Russia), equipped with NSG10 cantilevers (\"TipsNano\", Zelenograd, Russia; 47 to 150 kHz resonant frequency, 0.35 to 6.1 N/m force constant). The calibration of the microscope by height was carried out on a TGZ1 calibration grating (NT-MDT, Zelenograd, Russia; step height 21.4 \(\pm\) 1.5 nm). The total number of measured particles in each sample was no less than 200, and the number of frames for each sample was no less than 10.