未取代和O-乙酰化N-乙酰神经氨酸甲基酮糖苷酸水解的动力学研究。
Kinetic studies on the acid hydrolysis of the methyl ketoside of unsubstituted and O-acetylated N-acetylneuraminic acid.
作者信息
Neuberger A, Ratcliffe W A
出版信息
Biochem J. 1973 Aug;133(4):623-8. doi: 10.1042/bj1330623.
The hydrolysis of the model compound 2-O-methyl-4,7,8,9-tetra-O-acetyl-N-acetyl-alpha-d-neuraminic acid and neuraminidase (Vibrio cholerae) closely resembled that of the O-acetylated sialic acid residues of rabbit Tamm-Horsfall glycoprotein. This confirmed that O-acetylation was responsible for the unusually slow rate of acid hydrolysis of O-acetylated sialic acid residues observed in rabbit Tamm-Horsfall glycoprotein and their resistance to hydrolysis by neuraminidase. The first-order rate constant of hydrolysis of 2-methyl-N-acetyl-alpha-d-neuraminic acid by 0.05m-H(2)SO(4) was 56-fold greater than that of 2-O-methyl-4,7,8,9-tetra-O-acetyl-N-acetyl -alpha-d-neuraminic acid. Kinetic studies have shown that in the pH range 1.00-3.30, the observed rate of hydrolysis of 2-methyl-N-acetyl-alpha-d-neuraminic acid can be attributed to acid-catalysed hydrolysis of the negatively charged CO(2) (-) form of the methyl ketoside.
模型化合物2-O-甲基-4,7,8,9-四-O-乙酰基-N-乙酰基-α-d-神经氨酸与神经氨酸酶（霍乱弧菌）的水解过程与兔Tamm-Horsfall糖蛋白的O-乙酰化唾液酸残基的水解过程极为相似。这证实了O-乙酰化是导致兔Tamm-Horsfall糖蛋白中O-乙酰化唾液酸残基酸水解速度异常缓慢及其对神经氨酸酶水解具有抗性的原因。0.05m-H₂SO₄对2-甲基-N-乙酰基-α-d-神经氨酸的一级水解速率常数比2-O-甲基-4,7,8,9-四-O-乙酰基-N-乙酰基-α-d-神经氨酸的一级水解速率常数大56倍。动力学研究表明，在pH值为1.00 - 3.30的范围内，观察到的2-甲基-N-乙酰基-α-d-神经氨酸的水解速率可归因于甲基酮糖苷带负电荷的CO₂⁻形式的酸催化水解。
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