final step can actually take place in which a water molecule can actually cleave this red Bond the high in energy thioester bond between the sulfur and this carbon and in the process to stimulate the Second Step hydrolysis this residue the histogen 274 once again donates the H ion onto this oxygen and that promotes the hydrolysis of the cital COA in into that citrate molecule so the citral coenzyme a complex is stabilized via these interactions shown in this region here and in the final step which is not shown in the diagram we see that the histogen 274 will act as an H+ donor giving that H ion onto this oxygen of the carbonal group and that will allow it will stimulate the hydrolysis of the red bond to ultimately for the citrate molecule and release that co-enzyme a so this is Step number one of the citric acid cycle