Gallagher J T, Walker A, Lyon M, Evans W H
Cancer Research Campaign Department of Medical Oncology, Christie Hospital, University of Manchester, U.K.
Biochem J. 1988 Mar 15;250(3):719-26. doi: 10.1042/bj2500719.
An endoglycosidase is described in isolated liver plasma membranes that brings about a rapid and selective degradation of membrane-associated heparan sulphate, pre-labelled biosynthetically with Na2(35)SO4. The enzyme attacked mainly the polysaccharide chains of a hydrophobic membrane proteoglycan and it had little effect on a proteoglycan that could be displaced from the membranes with 1.0 M-NaCl. The highest activity was measured in the pH range 7.5-8.0, and the enzyme was almost completely inhibited below pH 5.5. Breakdown of susceptible polysaccharide chains was fast, being complete in 20-30 min. The major oligosaccharide fraction (Mr approx. 6000) produced by the enzyme was considerably smaller than the intact heparan sulphate chains. Enzyme activity was retained in membranes solubilized in 1% (v/v) Triton X-100. The high pH optimum and plasma-membrane association distinguish this enzyme from other heparan sulphate-degrading endoglycosidases that have acid pH optima and may be of lysosomal origin. A plasma-membrane endoglycosidase could modulate cellular interactions mediated by heparan sulphate, and/or release biologically active fragments of the polysaccharide from the cell periphery.
在分离的肝细胞膜中发现了一种内切糖苷酶，它能快速、选择性地降解与膜相关的硫酸乙酰肝素，该硫酸乙酰肝素是预先用Na2(35)SO4进行生物合成标记的。这种酶主要作用于一种疏水性膜蛋白聚糖的多糖链，而对能用1.0M NaCl从膜上置换下来的蛋白聚糖几乎没有影响。在pH值7.5 - 8.0范围内测得的活性最高，在pH值低于5.5时该酶几乎完全被抑制。易降解的多糖链的分解很快，20 - 30分钟内即可完成。该酶产生的主要寡糖组分（分子量约为6000）比完整的硫酸乙酰肝素链小得多。酶活性保留在溶解于1%（v/v） Triton X - 100中的膜中。高pH最佳值和与质膜的结合使这种酶与其他具有酸性pH最佳值且可能起源于溶酶体的硫酸乙酰肝素降解内切糖苷酶不同。质膜内切糖苷酶可以调节由硫酸乙酰肝素介导的细胞相互作用，和/或从细胞周边释放多糖的生物活性片段。
