Conlon J M, Abdel-Wahab Y H, O'Harte F P, Nielsen P F, Whittaker J
Regulatory Peptide Center, Department of Biomedical Sciences, Creighton University School of Medicine, Omaha, Nebraska 68178-0405, USA.
Endocrinology. 1998 Aug;139(8):3442-8. doi: 10.1210/endo.139.8.6139.
Insulin and four peptides derived from the posttranslational processing of proglucagon have been isolated in pure form from the pancreas of the cane toad, Bufo marinus. Although Bufo insulin contains 9 amino acid substitutions, compared with human insulin, all those residues that are considered to be involved in receptor-binding and in dimer and hexamer formation have been conserved. Bufo insulin was, however, more potent (4-fold) than human insulin in inhibiting the binding of [125I-Tyr-A14] insulin to the soluble full-length recombinant human insulin receptor, which is probably a consequence of the substitution (Thr --> His) at position A-8. Bufo glucagon was isolated in two molecular forms: glucagon-29 shows only one amino acid substitution (Thr29 --> Ser), compared with human glucagon; and glucagon-36 comprises glucagon-29, extended from its C-terminus by Lys-Arg-Ser-Gly-Gly-Met-Ser. The human proglucagon gene contains one copy of glucagon-like peptide (GLP)-1, a potent insulin secretogogue, and one copy of GLP-2 that is devoid of insulin-releasing activity. In contrast, two proglucagon-derived peptides with 32- and 37-amino acid residues (GLP-32 and GLP-37), displaying greater structural similarity to human GLP-1 than to GLP-2, were isolated from Bufo pancreas. Both peptides produced concentration-dependent increases in insulin release from glucose-responsive rat insulinoma-derived BRIN-BD11 cells. The threshold concentrations producing a significant (P < 0.001) effect were 10(-8) M (GLP-32) and 10(-9) M (GLP-37), and the maximum increase in the rate of insulin release produced by 10(-6) M concentrations of both peptides was approximately 5-fold.
胰岛素和四种源自胰高血糖素原翻译后加工的肽已从海蟾蜍（Bufo marinus）的胰腺中以纯形式分离出来。尽管与人类胰岛素相比，海蟾蜍胰岛素含有9个氨基酸替换，但所有被认为参与受体结合以及二聚体和六聚体形成的残基都得以保留。然而，在抑制[125I-酪氨酸-A14]胰岛素与可溶性全长重组人胰岛素受体的结合方面，海蟾蜍胰岛素比人类胰岛素更有效（4倍），这可能是A-8位替换（苏氨酸→组氨酸）的结果。海蟾蜍胰高血糖素以两种分子形式被分离出来：与人类胰高血糖素相比，胰高血糖素-29仅显示一个氨基酸替换（苏氨酸29→丝氨酸）；胰高血糖素-36由胰高血糖素-29组成，其C末端延伸有赖氨酸-精氨酸-丝氨酸-甘氨酸-甘氨酸-甲硫氨酸-丝氨酸。人类胰高血糖素原基因包含一个胰高血糖素样肽（GLP）-1拷贝，一种强效胰岛素分泌促进剂，以及一个缺乏胰岛素释放活性的GLP-2拷贝。相比之下，从海蟾蜍胰腺中分离出两种具有32和37个氨基酸残基的胰高血糖素衍生肽（GLP-32和GLP-37），它们与人类GLP-1的结构相似性高于GLP-2。两种肽都能使源自葡萄糖反应性大鼠胰岛素瘤的BRIN-BD11细胞的胰岛素释放呈浓度依赖性增加。产生显著（P<0.001）效应的阈值浓度分别为10^(-8)M（GLP-32）和10^(-9)M（GLP-37），两种肽在10^(-6)M浓度下产生的胰岛素释放速率最大增加约为5倍。
