succinyl coenzyme a synthetase (scs, also known as succinyl-coa synthetase or succinate thiokinase or succinate-coa ligase) is an enzyme that catalyzes the reversible reaction of succinyl-coa to succinate. the enzyme facilitates the coupling of this reaction to the formation of a nucleoside triphosphate molecule (either gtp or atp) from an inorganic phosphate molecule and a nucleoside diphosphate molecule (either gdp or adp). it plays a key role as one of the catalysts involved in the citric acid cycle, a central pathway in cellular metabolism, and it is located within the mitochondrial matrix of a cell.