Swank R T, Moore K, Chapman V M
Biochem Genet. 1987 Feb;25(1-2):161-74. doi: 10.1007/BF00498959.
Liver beta-glucuronidase is structurally altered in inbred strain PAC so that a peptide subunit with a more basic isoelectric point, GUS-SN, is produced. This allele of beta-glucuronidase was transferred to strain C57BL/6J by 12 backcross matings to form the congenic line B6 X PAC-Gus(n). Liver beta-glucuronidase activity was halved in males of the congenic strain compared to normal males. The lowered activity was specifically accounted for by a decrease in the lysosomal component. There was no alteration in the concentration of microsomal activity. This alteration in the subcellular distribution of beta-glucuronidase in Gus(n)/Gus(n) mice was confirmed by two independent gel electrophoretic systems which separate microsomal and lysosomal components. beta-Glucuronidase activity was likewise approximately halved in mutant spleen, lung, and brain, organs which contain exclusively or predominantly lysosomal beta-glucuronidase. The loss of liver lysosomal beta-glucuronidase activity was shown by immunotitration to be due to a decrease in the number of beta-glucuronidase molecules in lysosomes of the congenic strain. The Gus(n) structural alteration likely causes the lowered lysosomal beta-glucuronidase activity since the two traits remain in congenic animals. Heterozygous Gus(n)/Gus(b) animals had intermediate levels of liver beta-glucuronidase. Also, the effect was specific, in that three other lysosomal enzymes were not reproducibly lower in Gus(n)/Gus(n) mice. Gus(n) is, therefore, an unusual example of a mutation which causes a change in the subcellular distribution of a two-site enzyme.
近交系PAC的肝脏β-葡萄糖醛酸酶在结构上发生了改变，从而产生了一种等电点更碱性的肽亚基GUS-SN。通过12次回交将β-葡萄糖醛酸酶的这个等位基因转移到C57BL/6J品系中，以形成同源系B6 X PAC-Gus(n)。与正常雄性相比，同源系雄性的肝脏β-葡萄糖醛酸酶活性减半。活性降低具体是由溶酶体成分的减少引起的。微粒体活性浓度没有改变。通过两种独立的凝胶电泳系统证实了Gus(n)/Gus(n)小鼠中β-葡萄糖醛酸酶亚细胞分布的这种改变，这两种系统可分离微粒体和溶酶体成分。在仅含有或主要含有溶酶体β-葡萄糖醛酸酶的突变脾脏、肺和脑中，β-葡萄糖醛酸酶活性同样大约减半。免疫滴定显示，同源系肝脏溶酶体β-葡萄糖醛酸酶活性的丧失是由于同源系溶酶体中β-葡萄糖醛酸酶分子数量的减少。由于这两个性状在同源动物中仍然存在，Gus(n)结构改变可能导致溶酶体β-葡萄糖醛酸酶活性降低。杂合子Gus(n)/Gus(b)动物的肝脏β-葡萄糖醛酸酶水平处于中间。此外，这种影响是特异性的，因为在Gus(n)/Gus(n)小鼠中，其他三种溶酶体酶并没有可重复地降低。因此，Gus(n)是一个不寻常突变的例子，它导致了一种双位点酶的亚细胞分布发生变化。
