Akai H
Third Department of Internal Medicine, Tohoku University School of Medicine, Sendai, Japan.
Nihon Naibunpi Gakkai Zasshi. 1988 Oct 20;64(10):1065-80. doi: 10.1507/endocrine1927.64.10_1065.
Big gastrin comprising 34 amino acid residues (G34) consists of an N-terminal pentadecapeptide linked via two lysine residues to a C-terminal heptadecapeptide identical with little gastrin (G17). Both G17 and G34 have now been established as the principal active forms of gastrin. In this study, release of G34 N-terminal peptide fragment of methacholine and porcine gastrin releasing peptide (pGRP) stimulation in isolated rat stomach perfusion system was investigated by radioimmunoassay with use of an antiserum specific to the N-terminal portion of G34. G34 N-terminal immunoreactivity (IR-G34-N) was detected in rat stomach and proximal duodenum, and the highest concentration was found in extract of the antral mucosa. The concentration of IR-G34-N was constantly lower than that of IR-G17. By gel-filtration study, IR-G34-N in antral mucosa extract was attributed mostly to the G34 N-terminal pentadecapeptide-like component, and the concentration of G34 was about one tenth of G17. Methacholine 10(-8)-10(-3) M produced a biphasic dose-dependent release of IR-G34-N from the vascularly perfused isolated rat stomach. The maximal release was shown by 10(-5) M of methacholine. The release was concomitant with that of IR-G17 during methacholine stimulation. Stimulation of pGRP (14-27) (10(-7) M) produced a monophasic release of IR-G34-N from the vascularly perfused isolated rat stomach. The release was concomitant with that of G17 during the stimulation. The integrated IR-G34-N release was not stoichiometric with that of IR-G17, and IR-G34-N was constantly low. Gel-filtration of the perfusate from rat stomach revealed the presence of the G34 N-terminal pentadecapeptide-like component as a sole major component. The present results demonstrate that post-translational processing of the gastrin precursor in the rat antrum did not necessarily produce G34, which is further converted in the tissue to G17-related peptide(s) and that the G34 N-terminal fragment formed in the G34 conversion is stored and released concomitantly with G17-related peptide(s).
由34个氨基酸残基组成的大胃泌素（G34）由一个N端十五肽通过两个赖氨酸残基与一个C端十七肽相连组成，该C端十七肽与小胃泌素（G17）相同。现在已经确定G17和G34都是胃泌素的主要活性形式。在本研究中，利用对G34 N端部分具有特异性的抗血清，通过放射免疫测定法研究了在离体大鼠胃灌注系统中，乙酰甲胆碱和猪胃泌素释放肽（pGRP）刺激下G34 N端肽片段的释放情况。在大鼠胃和十二指肠近端检测到了G34 N端免疫反应性（IR-G34-N），在胃窦黏膜提取物中浓度最高。IR-G34-N的浓度始终低于IR-G17的浓度。通过凝胶过滤研究，胃窦黏膜提取物中的IR-G34-N主要归因于G34 N端十五肽样成分，G34的浓度约为G17的十分之一。10(-8)-10(-3) M的乙酰甲胆碱可使血管灌注的离体大鼠胃产生双相剂量依赖性的IR-G34-N释放。最大释放量出现在10(-5) M的乙酰甲胆碱时。在乙酰甲胆碱刺激过程中，IR-G34-N的释放与IR-G17的释放同时发生。刺激pGRP（14-27）（10(-7) M）可使血管灌注的离体大鼠胃产生单相的IR-G34-N释放。在刺激过程中，IR-G34-N的释放与G17的释放同时发生。IR-G34-N的综合释放与IR-G17的释放并非化学计量关系，且IR-G34-N的含量始终较低。对大鼠胃灌注液进行凝胶过滤显示，G34 N端十五肽样成分是唯一的主要成分。目前的结果表明，大鼠胃窦中胃泌素前体的翻译后加工不一定产生G34，G34在组织中会进一步转化为与G17相关的肽，并且在G34转化过程中形成的G34 N端片段与与G17相关的肽一起储存和释放。
