Marina A, Bravo J, Fita I, Rubio V
Instituto de Investigaciones Citológicas de la Fundación Valenciana de Investigaciones Biomédicas (Centro Asociado del CSIC), Spain.
Proteins. 1995 Jun;22(2):193-6. doi: 10.1002/prot.340220213.
Carbamoyl phosphate synthetase I (ammonia; E C 6.3.4.16) was purified from the liver of Rana catesbeiana (bullfrog). Crystals of the protein have been obtained at 22 degrees C by the hanging drop vapor diffusion technique, with polyethylene glycol as precipitant. Tetragonal crystals of about 0.3 x 0.3 x 0.7 mm diffract at room temperature to at least 3.5 A using a conventional source and are stable to X-radiation for about 12 h. Therefore, these crystals are suitable for high resolution studies. The space group is P4(1)2(1)2 (or its enantiomorph P4(3)2(1)2), with unit cell dimensions a = b = 291.6 A and c = 189.4 A. Density packing considerations are consistent with the presence of 4-6 monomers (M(r) of the monomer, 160,000) in the asymmetric unit. Amino-terminal sequence of the enzyme and of a chymotryptic fragment of 73.7 kDa containing the COOH-terminus has been obtained. The extensive sequence identity with rat and human carbamoyl phosphate synthetase I indicates the relevance for mammals of structural data obtained with the frog enzyme.
氨甲酰磷酸合成酶I（氨；EC 6.3.4.16）从牛蛙（Rana catesbeiana）的肝脏中纯化得到。利用悬滴气相扩散技术，以聚乙二醇作为沉淀剂，在22℃获得了该蛋白的晶体。使用传统光源，尺寸约为0.3×0.3×0.7 mm的四方晶体在室温下衍射至至少3.5 Å，并且对X射线辐射稳定约12小时。因此，这些晶体适合进行高分辨率研究。空间群为P4(1)2(1)2（或其对映体P4(3)2(1)2），晶胞参数a = b = 291.6 Å，c = 189.4 Å。密度堆积分析表明不对称单元中存在4 - 6个单体（单体的Mr为160,000）。已获得该酶的氨基末端序列以及包含羧基末端的73.7 kDa胰凝乳蛋白酶片段的序列。与大鼠和人类氨甲酰磷酸合成酶I的广泛序列同一性表明用青蛙酶获得的结构数据对哺乳动物具有相关性。
