RADIOISOTOPIC ASSAY OF ASPARTATE AND ALANINE AMINOTRANSFERASE

The activities of aspartate and alanine aminotransferases in biological samples were assessed through a novel and sensitive procedure, based on the conversion of [U-C-14]2-ketoglutarate to L-[U-C-14]glutamate. In human plasma, the generation of L-[U-C-14]glutamate was proportional to the volume of plasma (20-60-mu-L) and to the length of incubation (30-90 min). The reaction velocity was related to the temperature with a Q10 close to 1.7 for aspartate aminotransferase and 2.0 for alanine aminotransferase. At 37-degrees-C, the 95% confidence interval in healthy subjects ranged from 5.1-18.8 U/mL (mean value 11.9 U/L) for aspartate aminotransferase and from zero to 20.1 U/L (mean value 9.9 U/L) for alanine aminotransferase. The intra-assay coefficient of variation did not exceed 2.5%. The present method was also applied to homogenates prepared from rat pancreatic islets, liver, heart, parotid glands, and erythrocytes, using no more than 40-mu-g wet weight of tissue per sample, and could thus be used in small biological samples, such as those obtained by needle biopsy.