Winge D R, Nielson K B, Zeikus R D, Gray W R
J Biol Chem. 1984 Sep 25;259(18):11419-25.
Metallothionein was purified from the livers of adult and neonatal rats. The complete amino acid sequences of isoforms I and II of Cd-induced adult metallothionein were determined by automated Edman degradation of CNBr and tryptic peptides of carboxymethylated proteins. Both isoproteins contain 61 residues, but differ at 12 of those positions. The positions of the 20 cysteinyl residues are invariant with respect to those in other known mammalian metallothioneins. Based on the following criteria, the two soluble and constitutive Zn-metallothionein isoforms from neonatal liver appear identical to their corresponding forms in the adult animal: 1) they behave identically on reverse-phase high-pressure liquid chromatography, anion-exchange chromatography and nondenaturing gel electrophoresis; 2) their amino acid compositions are the same within experimental error; and 3) their amino acid sequences are identical in the first 23 residues, even though isoforms I and II differ in 7 of those positions. It appears highly likely that isoforms from both neonatal and adult rats are encoded by the same genes, and therefore that the large age-dependent concentration differences seen in the liver must be due to variation in gene regulation.
金属硫蛋白是从成年大鼠和新生大鼠的肝脏中纯化得到的。通过对羧甲基化蛋白质的溴化氰肽段和胰蛋白酶肽段进行自动埃德曼降解，确定了镉诱导的成年金属硫蛋白同工型I和II的完整氨基酸序列。两种同型蛋白均含有61个残基，但在其中12个位置上有所不同。20个半胱氨酰残基的位置与其他已知哺乳动物金属硫蛋白中的位置一致。基于以下标准，新生肝脏中的两种可溶性组成型锌金属硫蛋白同工型与其成年动物中的相应形式似乎相同：1）它们在反相高压液相色谱、阴离子交换色谱和非变性凝胶电泳中的行为相同；2）在实验误差范围内，它们的氨基酸组成相同；3）即使同工型I和II在其中7个位置上不同，但它们的前23个残基的氨基酸序列相同。新生大鼠和成年大鼠的同工型很可能由相同的基因编码，因此肝脏中观察到的与年龄相关的巨大浓度差异必定是由于基因调控的变化所致。
