Our combined kinetic and modelling studies confirmed that, despite its peculiarities and seemingly different pH of operation from the majority of KstDs, AcmB catalyzes  The answer to the first question is related to the shape of the free energy profile obtained for AcmB. By considering it within the precision of computational methods (c.a. 1 kcal/mol), we found that both substitutions, at 2 and 1 positions, significantly reduced the reaction rate of the RHR. The free energy barriers are so close to each other that both of them have a significant impact on the RHR reaction rate. A detailed explanation of a similar situation can be found in our previous paper related to KstD1 from R. erythropolis .