Schauer R, Wember M
Biochemisches Institut der Universität zu Kiel.
Biol Chem Hoppe Seyler. 1989 Mar;370(3):183-90. doi: 10.1515/bchm3.1989.370.1.183.
The starfish Asterias rubens contains a soluble sialidase (1.4 mU/mg homogenate protein), which was purified over 500-fold to apparent homogeneity by ammonium sulfate precipitation, gel filtration and affinity chromatography on immobilized 2-deoxy-2,3-didehydroneuraminic acid. The native sialidase has a molecular mass of 230 kDa (gel filtration) and consists of 4 subunits of each 63 kDa, as determined by SDS-gel electrophoresis. Its isoelectric point is at pH 4.9, the activity is optimum at pH 4.2 and 37 degrees C, and it hydrolyses preferably 4-methylumbelliferyl-alpha-N-acetyl-neuraminic acid, followed by sialyllactose and glycoproteins. The hydrolysis rate is decreased or stopped by the presence of O-acetyl groups on the sialic-acid residue to be cleaved. N-Glycoloyl residues also retard enzyme action, as well as alpha(2-6) bonds when compared with alpha(2-3) linkages. This relatively stable enzyme is inhibited by mercury or copper ions, 2-deoxy-2,3-didehydro-N-acetylneuraminic acid and by the increase of ionic strength. The evolutionary significance of starfish sialidase is discussed.
红海盘车海星含有一种可溶性唾液酸酶（1.4 mU/mg匀浆蛋白），通过硫酸铵沉淀、凝胶过滤以及在固定化2-脱氧-2,3-二脱氢神经氨酸上进行亲和层析，该酶被纯化了500多倍，达到表观均一性。天然唾液酸酶的分子量为230 kDa（凝胶过滤法测定），由4个各为63 kDa的亚基组成，这是通过SDS-凝胶电泳确定的。其等电点为pH 4.9，在pH 4.2和37℃时活性最佳，它优先水解4-甲基伞形酮基-α-N-乙酰神经氨酸，其次是唾液乳糖和糖蛋白。待切割的唾液酸残基上存在O-乙酰基会降低或停止水解速率。N-糖基酰基残基以及与α(2-3)连接相比的α(2-6)键也会阻碍酶的作用。这种相对稳定的酶会受到汞或铜离子、2-脱氧-2,3-二脱氢-N-乙酰神经氨酸以及离子强度增加的抑制。文中讨论了海星唾液酸酶的进化意义。
