ALT is a homodimeric cytoplasmic pyridoxal phosphate-dependent enzyme involved in cellular nitrogen metabolism, amino acid metabolism, and liver gluconeogenesis. Cayman’s Alanine Transaminase Assay provides a convenient method of detecting ALT activity in serum, plasma, tissue samples, and cell lysates. Measurement of the ALT activity is carried out by monitoring the rate of NADH oxidation in a coupled reaction system employing LDH. The oxidation of NADH to NAD+ is accompanied by a decrease in absorbance at 340 nm.