||Acetyl-CoA is widely present in animals, plants, microorganisms and cultured cells. It is an important intermediate metabolite produced during the metabolism of energy materials in organisms. It is a pivotal substance in the metabolism of energy substances in the body. The three major nutrients of sugar, fat, and protein converge into a common metabolic pathway-the tricarboxylic acid cycle and oxidative phosphorylation through acetyl-CoA. This pathway is completely oxidized to produce carbon dioxide and water, releasing energy for ATP synthesis. In addition, acetyl-CoA is a precursor substance for the synthesis of physiologically active substances such as fatty acids, ketone bodies, cholesterol and its derivatives. Malate dehydrogenase can catalyze malate and NAD to produce oxaloacetate and NADH. Citrate synthase can catalyze acetyl-CoA and oxaloacetate to produce citric acid and coenzyme A. Utilizing the coupling reaction of malate dehydrogenase and citrate synthase, the content of acetyl-CoA is directly proportional to the rate of NADH generation. The rising rate of absorbance at 340nm reflects the level of acetyl-CoA content.