Moss D W
Royal Postgraduate Medical School, Hammersmith Hospital, London, UK.
Clin Chim Acta. 1994 May;226(2):131-42. doi: 10.1016/0009-8981(94)90210-0.
Enzymes bound to the surfaces of cells may be retained by a hydrophobic amino acid sequence (e.g. gamma-glutamyltransferase) or by a specific glycan phosphatidylinositol (GPI) anchor (e.g. alkaline phosphatase). In either case the attachment is by means of non-covalent hydrophobic interactions between the anchoring domain of the enzyme and lipid components of the cell membrane. Enzyme molecules released into the plasma or bile, complete with their hydrophobic domains, can undergo aggregation and complexation to give rise to high molecular weight isoforms of gamma-glutamyltransferase or alkaline phosphatase. However, the GPI domain of alkaline phosphatase can be degraded by an inositol-specific phospholipase in plasma, but not in bile, with production of the hydrophobic, non-aggregating isoform of alkaline phosphatase that predominates in plasma.
与细胞表面结合的酶可能通过疏水氨基酸序列（如γ-谷氨酰转移酶）或特定的糖基磷脂酰肌醇（GPI）锚定物（如碱性磷酸酶）而被保留。在任何一种情况下，附着都是通过酶的锚定结构域与细胞膜脂质成分之间的非共价疏水相互作用实现的。释放到血浆或胆汁中的酶分子，连同其疏水结构域，可发生聚集和络合，从而产生γ-谷氨酰转移酶或碱性磷酸酶的高分子量同工型。然而，碱性磷酸酶的GPI结构域可被血浆中的肌醇特异性磷脂酶降解，但在胆汁中不会，从而产生在血浆中占主导地位的疏水、非聚集性碱性磷酸酶同工型。
