Figure 4.

Differential effect of Cl⁻ anions and Na⁺ cations on MtP5CR activity. To reduce the carryover of ions in the standard reaction mixture, the enzyme was assayed in the presence of 0.2 mM L-P5C (in 20 mM Tris-HCl buffer pH 7.5) with either 1 mM NADH or 0.5 mM NADPH as the electron donor. To avoid unspecific effects due to pH variations, after fixing the desired concentration of Cl⁻ and Na⁺ ions, the pH was brought to pH 7.75 with Tris base or tricine, respectively. Three replications were carried out for each treatment. Non-linear regression analysis of data [log(inhibitor) vs. normalized response-Variable slope for enzyme inhibition; log(agonist) vs. normalized response-Variable slope for enzyme stimulation] was computed using Prism 6 for Windows, version 6.03.