Saxena A, Raveh L, Ashani Y, Doctor B P
Division of Biochemistry, Walter Reed Army Institute of Research, Washington, DC 20307-5100, USA.
Biochemistry. 1997 Jun 17;36(24):7481-9. doi: 10.1021/bi963156d.
Cholinesterases are serine hydrolases that can potentially be used as pretreatment drugs for organophosphate toxicity, as drugs to alleviate succinylcholine-induced apnea, and as detoxification agents for environmental toxins such as heroin and cocaine. The successful application of serum-derived cholinesterases as bioscavengers stems from their relatively long residence time in the circulation. To better understand the relationship between carbohydrate structure and the stability of cholinesterases in circulation, we determined the monosaccharide composition, the distribution of various oligosaccharides, and the structure of the major asparagine-linked oligosaccharides units present in fetal bovine serum acetylcholinesterase and equine serum butyrylcholinesterase. Our findings indicate that 70-80% of the oligosaccharides in both enzymes are negatively charged. This finding together with the molar ratio of galactose to sialic acid clearly suggests that the beta-galactose residues are only partially capped with sialic acid, yet they displayed a long duration in circulation. The structures of the two major oligosaccharides from fetal bovine serum acetylcholinesterase and one major oligosaccharide from equine serum butyrylcholinesterase were determined. The three carbohydrate structures were of the biantennary complex type, but only the ones from fetal bovine serum acetylcholinesterase were fucosylated on the innermost N-acetylglucosamine residue of the core. Pharmacokinetic studies with native, desialylated, and deglycosylated forms of both enzymes indicate that the microheterogeneity in carbohydrate structure may be responsible, in part, for the multiphasic clearance of cholinesterases from the circulation of mice.
胆碱酯酶是丝氨酸水解酶，有潜力用作有机磷中毒的预处理药物、缓解琥珀酰胆碱诱导的呼吸暂停的药物以及海洛因和可卡因等环境毒素的解毒剂。血清来源的胆碱酯酶作为生物清除剂的成功应用源于它们在循环系统中相对较长的停留时间。为了更好地理解碳水化合物结构与胆碱酯酶在循环中的稳定性之间的关系，我们测定了胎牛血清乙酰胆碱酯酶和马血清丁酰胆碱酯酶中存在的单糖组成、各种寡糖的分布以及主要天冬酰胺连接寡糖单元的结构。我们的研究结果表明，两种酶中70 - 80%的寡糖带负电荷。这一发现与半乳糖与唾液酸的摩尔比清楚地表明，β -半乳糖残基仅部分被唾液酸封端，但它们在循环中显示出较长的持续时间。确定了胎牛血清乙酰胆碱酯酶的两种主要寡糖和马血清丁酰胆碱酯酶的一种主要寡糖的结构。这三种碳水化合物结构均为双天线复合型，但只有胎牛血清乙酰胆碱酯酶的结构在核心最内层的N - 乙酰葡糖胺残基上被岩藻糖基化。对两种酶的天然、去唾液酸化和去糖基化形式进行的药代动力学研究表明，碳水化合物结构的微观异质性可能部分导致了胆碱酯酶从小鼠循环中多相清除。
