Desbuguois B
Eur J Biochem. 1975 Dec 15;60(2):335-47. doi: 10.1111/j.1432-1033.1975.tb21008.x.
Acetylated derivatives of glucagon have been prepared by reacting this hormone under various conditions with acetic anhydride. They have been chemically characterized by the use of a 14C-labeled reagent, by peptide mapping techniques following hydrolysis by pronase and chymotrypsin, and by spectroscopy. Acetylation in sodium acetate (pH 5.5) results in a full substitution of the alpha-amino group of the N-terminal histidyl residue, but in a partial (about 0.3 acetyl group per residue) substitution of the epsilon-amino group of the lysyl residue 12. The monosubstituted (on the alpha-amino group) and the disubstituted (on both amino groups) acetylated components have been separated by chromatography on DEAE-cellulose and CM-cellulose. Acetylation in sodium bicarbonate (pH 8.0) results in a complete substitution of both amino groups and of the hydroxyl groups of the tyrosyl residues 10 and 13. Complete deacetylation of the O-acetyltyrosyl residues occurs upon treatment with hydroxyl-amine. Mono, di and tetraacetylglucagon are homogeneous when analyzed by disc gel electrophoresis; di and tetrasubstituted derivatives show an increased mobility towards the anode. 125I-labeled derivatives of acetylglucagon show higher distribution coefficients in the aqueous two-phase dextran/poly(ethylene glycol) system than do similar derivatives of glucagon. Acetylation decreases in parallel the ability of glucagon to stimulate the activity of adenylate cyclase and to bind to its receptors in liver cell membranes of the rat. The biological potencies of the mono, di and tetrasubstituted derivates are, respectively, about 10, 1 and 0.1% that of native glucagon. The binding properties of the material dissociated from the acetylglucagon-receptor complex suggest that the reduction in biological activity results from a decrease in the intrinsic affinity of the modified glucagon for the receptors, as well as from the presence of small amounts of residual, unreacted glucagon. Studies with 125I-labeled derivatives of glucagon indicate that acetylation decreases the rate of association and increases the rate of dissociation of the hormone-receptor complex.
通过在各种条件下使胰高血糖素与乙酸酐反应制备了其乙酰化衍生物。利用14C标记试剂、在链霉蛋白酶和胰凝乳蛋白酶水解后采用肽图谱技术以及光谱学对其进行了化学表征。在乙酸钠（pH 5.5）中进行乙酰化会导致N端组氨酰残基的α-氨基完全被取代，但赖氨酸残基12的ε-氨基会部分被取代（每个残基约0.3个乙酰基）。单取代（在α-氨基上）和双取代（在两个氨基上）的乙酰化组分已通过DEAE-纤维素和CM-纤维素柱色谱法分离。在碳酸氢钠（pH 8.0）中进行乙酰化会导致两个氨基以及酪氨酸残基10和13的羟基完全被取代。用羟胺处理时，O-乙酰酪氨酸残基会完全脱乙酰化。通过圆盘凝胶电泳分析时，单乙酰、二乙酰和四乙酰胰高血糖素是均一的；双取代和四取代衍生物向阳极的迁移率增加。乙酰化胰高血糖素的125I标记衍生物在双水相葡聚糖/聚（乙二醇）系统中的分配系数比胰高血糖素的类似衍生物更高。乙酰化同时降低了胰高血糖素刺激腺苷酸环化酶活性以及与大鼠肝细胞膜上其受体结合的能力。单取代、双取代和四取代衍生物的生物活性分别约为天然胰高血糖素的10%、1%和0.1%。从乙酰化胰高血糖素-受体复合物解离的物质的结合特性表明，生物活性的降低是由于修饰后的胰高血糖素对受体的内在亲和力降低以及存在少量残留的未反应胰高血糖素所致。对胰高血糖素的125I标记衍生物的研究表明，乙酰化降低了激素-受体复合物的结合速率并增加了解离速率。
