Wraight C, Lingelbach K, Hoogenraad N
Eur J Biochem. 1985 Dec 2;153(2):239-42. doi: 10.1111/j.1432-1033.1985.tb09292.x.
Ornithine transcarbamylase (OTCase) was purified from the small intestine of rat and the properties of the gut enzyme were compared with those of the enzyme from liver. The enzymes from both sources bound to the transition-state analog inhibitor, delta-N-(phosphonoacetyl)-L-ornithine, immobilized on Sepharose and eluted with carbamyl phosphate as a homogeneous preparation. The specific activities of the pure enzymes were 966 mumol min-1 mg-1 and 928 mumol min-1 mg-1 from liver and gut respectively, and the molecular mass, based on electrophoretic mobility, was 38 000 Da. The isoelectric point of the enzymes from both sources was 7.3. The enzymes from both sources cross-react to the same extent with antibodies against the liver enzyme on Western transfers and the size of the mRNA was identical on Northern transfers probed with a cDNA for the liver enzyme. Although OTCase is apparently the same gene product in both liver and gut, the enzyme levels respond differently to alterations in the protein content of the diet. OTCase in liver increased from 0.76 mumol min-1 microgram-1 DNA on 15% casein to 1.3 mumol min-1 microgram-1 DNA on 60% casein (P less than 0.01) whereas in small intestine the level decreased from 8.8 nmol min-1 microgram DNA on 15% casein to 5.7 nmol min-1 microgram-1 DNA on 60% casein (P less than 0.05). When expressed on a fresh-weight basis, the enzyme activity in liver shows the characteristic increase with increasing protein, whereas the activity in gut does not. The connection between these differences in gene expression and the different physiological roles of OTCase in liver and gut is discussed.
从大鼠小肠中纯化出鸟氨酸转氨甲酰酶（OTCase），并将肠道酶的性质与肝脏来源的酶进行比较。两种来源的酶均与固定在琼脂糖上的过渡态类似物抑制剂δ-N-（膦酰乙酰基）-L-鸟氨酸结合，并以氨基甲酰磷酸作为均一制剂进行洗脱。纯化酶的比活性分别为：肝脏来源的为966 μmol min⁻¹ mg⁻¹，肠道来源的为928 μmol min⁻¹ mg⁻¹，基于电泳迁移率计算的分子量为38000 Da。两种来源的酶的等电点均为7.3。在蛋白质免疫印迹中，两种来源的酶与抗肝脏酶的抗体发生相同程度的交叉反应，在用肝脏酶的cDNA进行探针杂交的RNA印迹中，mRNA的大小相同。尽管OTCase在肝脏和肠道中显然是相同的基因产物，但酶水平对饮食中蛋白质含量的变化反应不同。肝脏中的OTCase从15%酪蛋白饮食时的0.76 μmol min⁻¹ μg⁻¹ DNA增加到60%酪蛋白饮食时的1.3 μmol min⁻¹ μg⁻¹ DNA（P＜0.01），而在小肠中，该水平从15%酪蛋白饮食时的8.8 nmol min⁻¹ μg DNA降至60%酪蛋白饮食时的5.7 nmol min⁻¹ μg⁻¹ DNA（P＜0.05）。以鲜重为基础表达时，肝脏中的酶活性呈现出随蛋白质增加而增加的特征，而肠道中的活性则不然。本文讨论了这些基因表达差异与OTCase在肝脏和肠道中不同生理作用之间的联系。
