Pfister K, Bosshard N, Zopfi M, Gitzelmann R
Department of Pediatrics, University of Zürich, Switzerland.
Biochem J. 1988 Nov 1;255(3):825-32. doi: 10.1042/bj2550825.
Three differently modified forms of beta-glucuronidase are known to exist: a microsomal enzyme form (M) existing in tissues where egasyn, a second microsomal protein, is present; and an acidic (La; complex-type oligosaccharide) and a basic (Lb; non-complex type oligosaccharide) lysosomal form which occur in all mouse tissues. Lb predominates in tissues containing microsomal beta-glucuronidase, La in those lacking it. In pulse-labelling experiments using mouse strain C57BL/6 liver containing egasyn (Eg+/Eg+) and microsomal enzyme, about half of the newly synthesized beta-glucuronidase was processed to the microsomal enzyme form, which was evidently further processed to Lb, and about half directly to La. In contrast, in liver of the congenic line C57BL/6.YBR Es-1b Eg0 that lacks egasyn (Eg0/Eg0) and microsomal enzyme, most of the labelled beta-glucuronidase was processed to La, and only a minor portion to Lb. Newly synthesized enzyme appeared first in microsomal, then in light and heavy lysosomal fractions of Eg+/Eg+ liver. In Eg0/Eg0 liver, no labelled enzyme was measurable in the microsomes, but it appeared rapidly in both types of lysosomes. Taken together these findings indicate that the microsomal enzyme form serves as a precursor of Lb, and that La is synthesized independently. The apparent half-life of La is only two-thirds that of Lb; this fact accounts for the reduced beta-glucuronidase activity in Eg0/Eg0 liver, which contains La as the predominant form.
已知存在三种不同修饰形式的β-葡萄糖醛酸酶：一种微粒体酶形式（M），存在于含有另一种微粒体蛋白egasyn的组织中；以及酸性（La；复合型寡糖）和碱性（Lb；非复合型寡糖）溶酶体形式，它们存在于所有小鼠组织中。Lb在含有微粒体β-葡萄糖醛酸酶的组织中占主导，La在缺乏该酶的组织中占主导。在使用含有egasyn（Eg+/Eg+）和微粒体酶的C57BL/6小鼠品系肝脏进行的脉冲标记实验中，大约一半新合成的β-葡萄糖醛酸酶被加工成微粒体酶形式，该形式显然进一步被加工成Lb，大约一半直接被加工成La。相比之下，在缺乏egasyn（Eg0/Eg0）和微粒体酶的同基因系C57BL/6.YBR Es-1b Eg0的肝脏中，大部分标记的β-葡萄糖醛酸酶被加工成La，只有一小部分被加工成Lb。新合成的酶首先出现在Eg+/Eg+肝脏的微粒体中，然后出现在轻、重溶酶体组分中。在Eg0/Eg0肝脏中，微粒体中未检测到标记酶，但它在两种类型的溶酶体中迅速出现。综合这些发现表明，微粒体酶形式是Lb的前体，而La是独立合成的。La的表观半衰期仅为Lb的三分之二；这一事实解释了以La为主要形式的Eg0/Eg0肝脏中β-葡萄糖醛酸酶活性降低的原因。
