Succinyl-CoA synthetase enzyme, molecular model. Also known as succinyl coenzyme A synthetase (SCS), this enzyme catalyses the reversible reaction between succinyl-CoA and succinic acid. This reaction and enzyme plays a central role in the citric acid cycle, one of the processes by which energy is harnessed on a cellular level. The molecule takes the form of a heterotetramer, represented by the four colours here. This form of the enzyme is found in the bacterium Escherichia coli.