Ozaki M, Terada K, Kanazawa M, Fujiyama S, Tomita K, Mori M
Department of Molecular Genetics, Kumamoto University School of Medicine, Japan.
Enzyme Protein. 1994;48(4):213-21. doi: 10.1159/000474991.
Carbamoylphosphate synthetase I (CPS I), a urea cycle enzyme, is located almost exclusively in the mitochondria of hepatocytes. The enzyme is unique in that it constitutes about 2-6% of total liver protein and is composed of a large subunit of 160 kD. We developed a sensitive enzyme-linked immunosorbent assay (ELISA) for measurement of the enzyme in plasma using an antibody against the rat enzyme. In galactosamine-induced rat acute hepatitis, plasma concentration of CPS I that was 1-2 micrograms/ml blood before the treatment, increased up to 125 micrograms/ml blood in 24 h after the treatment and decreased to a near control level in 72 h. Plasma concentration of ornithine carbamoyl-transferase (OCT), another urea cycle enzyme, reached a maximum in 24 h and then decreased a little more rapidly than that of CPS I. On the other hand, alanine aminotransferase activity reached a maximum in 36 h and decreased to a normal level in 96 h. In immunoblot analysis, the native CPS I polypeptide of 160 kD and its fragments of 140 and 125 kD were detected 24-48 h after the treatment. When purified rat CPS I and bovine OCT were injected intravenously into rats, the enzymes disappeared from blood roughly exponentially with apparent half-lives of about 67 and 18 min, respectively. Development of an ELISA for human CPS I and determination of the serum enzyme in various liver diseases remain to be performed.
氨甲酰磷酸合成酶I（CPS I）是一种尿素循环酶，几乎仅存在于肝细胞的线粒体中。该酶很独特，它占肝脏总蛋白的约2 - 6%，由一个160 kD的大亚基组成。我们利用针对大鼠该酶的抗体开发了一种灵敏的酶联免疫吸附测定法（ELISA）来检测血浆中的该酶。在半乳糖胺诱导的大鼠急性肝炎中，治疗前血浆CPS I浓度为1 - 2微克/毫升血液，治疗后24小时内升至125微克/毫升血液，72小时后降至接近对照水平。另一种尿素循环酶鸟氨酸氨甲酰转移酶（OCT）的血浆浓度在24小时达到峰值，然后下降速度比CPS I稍快。另一方面，丙氨酸转氨酶活性在36小时达到峰值，96小时降至正常水平。在免疫印迹分析中，治疗后24 - 48小时检测到160 kD的天然CPS I多肽及其140和125 kD的片段。当将纯化的大鼠CPS I和牛OCT静脉注射到大鼠体内时，这些酶从血液中大致呈指数消失，表观半衰期分别约为67分钟和18分钟。开发用于检测人CPS I的ELISA以及测定各种肝脏疾病中的血清酶仍有待进行。
