L-Ornithine-ketoacid-transaminase deficiency in cultured fibroblasts of a patient with hyperornithinaemia and gyrate atrophy of the choroid and retina.

L-Ornithine-ketoacid-transaminase deficiency was established in cultured fibroblasts obtained from a patient with hyperornithinaemia (mean ornithine level in serum approximately 100 mumol/l) and gyrate atrophy of the choroid and retina. The deficiency was found both the L-ornithine concentrations of 3.0 mM (about twice the KM value) and 12 mM, indicating that the enzymic defect was not due to a decreased affinity for this substrate. The reliability of the colorimetric assay of ornithine-ketoacid-transaminase activity was established radiochemically. Performance of the radiochemical assay revealed the presence of an impurity in the substrate DL-[2-14C]ornithine - HCl being a strong inhibitor of the enzyme. The passage level and the subcultivation time of the fibroblasts did not influence the enzymic activity.