Identification and Properties of Glycated Monoclonal

concentrated enzyme extracts with higher specific activities. By performing the assay in the presence of various concentrations of ornithine, we confirmed that AGAT is inhibited by ornithine, as reported previously (7 ). This observation may be of clinical interest in conditions of hyperornithinemia. Decreased brain creatine has been observed in patients affected with gyrate atrophy of the choroid and retina (McKusick 258870). It has been suggested that in this condition the high concentrations of ornithine caused by the inherited deficiency of ornithine-aminotransferase inhibit AGAT and, thus, creatine biosynthesis (8 ). In addition, in hyperornithinemia-hyperammonemia-homocitrullinuria syndrome, creatine excretion has been shown to be low (9 ) In our in vitro assay, the amount of ornithine formed posed no problem. Inhibition became significant at an ornithine concentration of 0.1 mmol/L (93% remaining activity), whereas during incubations over 20 h, at most 3 nmoles of ornithine were formed (0.015 mmol/L). It is known that creatine regulates AGAT at the pretranslational level. We investigated whether creatine also inhibits AGAT activity directly. We observed no inhibition of AGAT by creatine at concentrations up to 5 mmol/L. In conclusion, we present a sensitive and specific enzymatic assay for AGAT that enables enzymatic diagnosis of AGAT deficiency. It may help in the diagnosis of more patients with AGAT deficiency. Early recognition and treatment may effectively prevent neurologic damage (1 ).