Nagata N, Akaboshi I, Yamamoto J, Matsuda I, Ohtsuka H, Katsuki T
Pediatr Res. 1980 Dec;14(12):1370-3. doi: 10.1203/00006450-198012000-00022.
A radiochemical assay method of ornithine transcarbamylase (OTC) was developed using labeled carbamyl phosphate as a substrate. The enzyme activities determined by this method in peripheral white blood cells from ten normal subjects were 1.32 +/- 0.95 nmoles/mg/hr and the apparent Km's, when assayed at pH 8.5, were 6.4 mM for ornithine and 0.6 mM for carbamyl phosphate. On the contrary, the apparent Km's of human liver OTC were 0.6 mM for ornithine and 0.12 mM for carbamyl phosphate. The average OTC activity of granulocytes was 1.0 nmoles/mg/hr, whereas that of mononuclear cells was 0.4 mmoles/mg/hr. Lymphoid cell lines were established from three normal subjects and an OTC-deficient infant. All these cell lines demonstrated no OTC activity. When arginine was removed from the medium and replaced by ornithine, the lymphoid cells were unable to grow in culture. On autoradiography, the lymphoid cells showed labelling at incubation in the presence of 14C-citrulline, but not with 14C-ornithine.
采用标记的氨甲酰磷酸作为底物，建立了鸟氨酸转氨甲酰酶（OTC）的放射化学测定方法。用该方法测定的10名正常受试者外周血白细胞中的酶活性为1.32±0.95纳摩尔/毫克/小时，在pH 8.5条件下测定时，鸟氨酸的表观Km值为6.4毫摩尔，氨甲酰磷酸的表观Km值为0.6毫摩尔。相反，人肝脏OTC的表观Km值，鸟氨酸为0.6毫摩尔，氨甲酰磷酸为0.12毫摩尔。粒细胞的平均OTC活性为1.0纳摩尔/毫克/小时，而单核细胞的平均OTC活性为0.4毫摩尔/毫克/小时。从3名正常受试者和1名OTC缺乏的婴儿建立了淋巴细胞系。所有这些细胞系均未显示OTC活性。当从培养基中去除精氨酸并用鸟氨酸替代时，淋巴细胞在培养中无法生长。在放射自显影片上，淋巴细胞在14C-瓜氨酸存在下孵育时显示标记，但在14C-鸟氨酸存在下未显示标记。
