Sparkes R S, Weiss M C
Proc Natl Acad Sci U S A. 1973 Feb;70(2):377-81. doi: 10.1073/pnas.70.2.377.
The expression of alanine aminotransferase (EC 2.6.1.2), an enzyme that is inducible in the liver, has been examined in somatic hybrid cells formed by crossing well-differentiated rat hepatoma cells with rat diploid epithelial cells, the former characterized by high activity and inducibility of the enzyme, and the latter by the absence of detectable activity. The hybrid cells that contain essentially complete chromosomal sets of the two parents show only very low activity and little inducibility. Among numerous "segregated" hybrid subclones, which have lost up to 40% of the chromosomes initially present, several show expression of intermediate levels of enzyme activity and very little inducibility, and two independent subclones are characterized by full re-expression of both baseline and inducible enzyme activity. The electrophoretic mobility of the enzyme from the latter hybrids, from the hepatoma parental cells, and from rat liver is identical. The absence of a correlation between total chromosome number of the hybrid cells and re-expression of alanine aminotransferase suggests that the loss of specific chromosomes is required for re-expression. In these hybrid cells, the re-expression of alanine aminotransferase baseline and inducibility is independent of that of tyrosine aminotransferase inducibility.
丙氨酸转氨酶（EC 2.6.1.2）是一种在肝脏中可诱导的酶，已在由高分化大鼠肝癌细胞与大鼠二倍体上皮细胞杂交形成的体细胞杂种细胞中进行了检测。前者的特征是该酶具有高活性和可诱导性，而后者则没有可检测到的活性。含有两个亲本基本完整染色体组的杂种细胞仅表现出非常低的活性和很少的诱导性。在众多“分离”的杂种亚克隆中，这些亚克隆最多丢失了最初存在的40%的染色体，其中几个显示出中等水平的酶活性表达且诱导性很小，并且两个独立的亚克隆的特征是基线和诱导性酶活性都完全重新表达。来自后一种杂种、肝癌亲本细胞和大鼠肝脏的酶的电泳迁移率是相同的。杂种细胞的总染色体数与丙氨酸转氨酶的重新表达之间缺乏相关性，这表明重新表达需要特定染色体的丢失。在这些杂种细胞中，丙氨酸转氨酶基线和诱导性的重新表达与酪氨酸转氨酶诱导性的重新表达无关。
