A new sensitive and convenient assay of ornithine aminotransferase.

A new radioisotopic assay for ornithine aminotransferase with [U-14C]ornithine as a substrate was developed. The dihydroquinazolinium compound formed was extracted from the reaction mixture with n-butanol and an addition of high concentration of sodium sulfate. This assay is sensitive and convenient and more than 50 assays can be done in one day without any special apparatus. The activities of ornithine aminotransferase in rat liver and human lymphoblastoid cells could be measured at nanomole levels by this method. Thus, the assay should be useful for measurement of OAT activity in cultured cells and for studies on the metabolic bases of the different types of ornithine aminotransferase deficiency: vitamin B6-responsive and -nonresponsive types.