## 2 Materials and Methods
### Experimental Setup for the Study of the Effect of the PEMF  
The experimental setup was analogous to that described in detail by [PERSON] et al. [56]. The setup represented an ultra-short electromagnetic pulse emitter, which comprised of a semiconductor-based high-voltage pulse generator (HVPG; FID GmbH, Burbach, Germany) and an antenna-feeder device (AFD), based on an array of 500 mm-long transverse electromagnetic (TEM) horn antennas. The working area, where the samples to be irradiated were placed, was located within the antenna mouth, as shown in Figure 1A.  
The USEMP parameters were controlled with an IPPL-L converter of pulsed electric field strength (VNIOFI, Moscow, Russia) [57, 58, 59].  
The HVPG was intended for the excitation of the antenna array. The HVPG output was matched with the input of the antenna array. The dimensions of the working area were 400 \(\times\) 500 mm.  
In the working area of the emitter, the intensity of the pulsed electric field was measured. The pulses were recorded with an IPPL-L converter (conversion factor 5.11 \(\times\) 10\({}^{-4}\) V/(V/m), transient characteristic rise-time 5 ps, transient characteristic duration 4.6 ns), and a stroboscopic oscillograph (50 GHz bandpass). Figure 1B displays an oscillogram of the ultra-short electromagnetic pulses recorded within the antenna mouth in the point, where the test tube--with the solution to be irradiated--was placed.  
A test tube, containing 0.1 uM (10\({}^{-7}\) M) HRP solution in 2 mM potassium phosphate buffer (pH 7.4), was placed within the working area of the emitter (Figure 1A). The strength of the pulsed electromagnetic field at this point was 640 kV/m, while the pulse repetition rate was 16 Hz.  
The energy supplied to the HRP enzyme solution was calculated using the equation [3]:  
\[P(t)=[E(t)\times H(t)]=\frac{E^{2}(t)}{377} \tag{1}\]  
where \(E(t)\) and \(H(t)\) are the instantaneous values of the strength of the electric and magnetic fields, respectively. The transition only to the instantaneous value of the electric field is valid for losses in a medium, where the ratio \(E/H=377\) (characteristic impedance of vacuum) is observed. The energy \(W\), supplied to the irradiated object with the area \(S\) in one pulse, is calculated using the following equation:  
\[W=S\int_{0}^{T}\frac{E^{2}(t)}{377}dt \tag{2}\]  
Figure 1: Schematic representation of the working area of the PEMF experimental setup (**A**); and oscillogram of the ultra-short electromagnetic pulses recorded within the antenna mouth in the point, where the test tube with the PEMF-irradiated solution was placed (**B**). In A, the thin-end arrows indicate the main units of the experimental setup: the HVPG (high-voltage pulse generator), the AFD (antenna-feeder device), the test tube containing the sample to be irradiated, and the TEM horn antenna. \(\overrightarrow{E}\) is the direction of the electric field strength vector, indicated by the thick-end arrow. The length of the TEM horn antenna is 500 mm.  
The average power supplied to the area \(S\) depends on the pulse repetition rate \(F\) as follows:  
\[<\)\(P\)\(>\) = \(W\cdot F\) (3)  
Based on the calculation technique described in [3], given \(E\) = 640 kV/m, one can obtain that the energy supplied with one pulse makes up \(1.3\times 10^{-4}\) J, while the average power for a period at 16 Hz frequency amounts to \(2.1\times 10^{-3}\) W.