STRUCTURE OF GLYCAN MOIETIES RESPONSIBLE FOR THE EXTENDED CIRCULATORYLIFE TIME OF FETAL BOVINE SERUM ACETYLCHOLINESTERASE AND EQUINE SERUMBUTYRYLCHOLINESTERASE

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 envir onmental toxins such as heroin and cocaine. The successful application of serum-derived cholinesterases as bioscavengers stems from their re latively long residence rime in the circulation. To better understand the relationship between carbohydrate structure and the stability of c holinesterases in circulation, we determined the monosaccharide compos ition, the distribution of various oligosaccharides, and the structure of the major asparagine-linked oligosaccharides units present in feta l bovine serum acetylcholinesterase and equine serum butyrylcholineste rase. Our findings indicate that 70-80% of the oligosaccharides in bot h enzymes are negatively charged. This finding together with the molar ratio of galactose to sialic acid clearly suggests that the beta-gala ctose residues structures of the two major oligosaccharides from fetal bovine serum acetylcholinesterase and one major oligosaccharide from equine serum butyrylcholinesterase were determined. The three carbohyd rate structures were of the biantennary complex type, but only the one s from fetal bovine serum acetylcholinesterase were fucosylated on the innermost N-acetylglucosamine residue of the core. Pharmacokinetic st udies with native, desialylated, and deglycosylated forms of both enzy mes indicate that the microheterogeneity in carbohydrate structure may be responsible, in part, for the multiphasic clearance of cholinester ases from the circulation of mice.