Carraway R E, Singer E A, Ferris C F, Mitra S P
Adv Exp Med Biol. 1986;198 Pt B:169-79. doi: 10.1007/978-1-4757-0154-8_21.
Treatment of mammalian plasmas with pepsin yielded extraordinary quantities of immunoreactive neurotensin (iNT) and methionine5-enkephalin (iENK). The concentrations measured after pepsin-treatment (iNT, 1-5 microM and iENK, 0.1-0.5 microM) were 1-100 thousand times the normal circulating levels of these peptides. The reactions were shown to be time, temperature and pH dependent and to involve the action of pepsin on albumin-like proteins (Mr, ca, 65,000). Pepsin-generated iNT from rat plasma differed from NT since it reacted only with C-terminal directed antisera and eluted earlier than NT during HPLC on mu-Bondapak C-18. Partially purified iNT was active in two bioassays for NT, one which senses changes in vascular permeability to protein after intradermal injection into rats and another which measures release of histamine from isolated rat mast cells. Other biologic activities generated by pepsin-treating plasma included effects on systemic blood pressure in rats and on the contractility of the isolated guinea pig ileum. Some of these, however, were attributable to the formation of angiotensin- and bradykinin-related peptides. Pepsin-generated iENK gave three major peaks during HPLC, one of which (ca, 25%) co-eluted with oxidized ENK and also registered in a radioreceptor assay for opiate-related substances. In addition, this material produced ENK-like effects on the isolated guinea pig ileum and on vascular permeability in rat skin. The precursor-like protein(s) for iENK were distinguished from adrenal proenkephalins since it did not liberate iENK upon digestion with trypsin and carboxypeptidase B. Since pepsin can mimic renin these results suggest the existence of systems in blood (analogous to the renin/angiotensin system) for the generation of biologically active NT- and ENK-related peptides and they also raise the question as to whether other neuropeptides might be found circulating in precursor form(s).
用胃蛋白酶处理哺乳动物血浆可产生大量具有免疫反应性的神经降压素（iNT）和蛋氨酸5-脑啡肽（iENK）。胃蛋白酶处理后测得的浓度（iNT为1 - 5微摩尔/升，iENK为0.1 - 0.5微摩尔/升）是这些肽正常循环水平的1万至10万倍。结果表明，这些反应与时间、温度和pH值有关，且涉及胃蛋白酶对类白蛋白（分子量约65,000）的作用。胃蛋白酶从大鼠血浆中产生的iNT与神经降压素（NT）不同，因为它仅与C末端定向抗血清反应，且在μ-Bondapak C-18柱上进行高效液相色谱（HPLC）时比NT洗脱得早。部分纯化的iNT在两种检测NT的生物测定中具有活性，一种是在大鼠皮内注射后检测血管对蛋白质通透性的变化，另一种是测量从分离的大鼠肥大细胞中组胺的释放。胃蛋白酶处理血浆产生的其他生物学活性包括对大鼠全身血压和分离的豚鼠回肠收缩性的影响。然而，其中一些作用可归因于血管紧张素和缓激肽相关肽的形成。胃蛋白酶产生的iENK在HPLC过程中出现三个主要峰，其中一个峰（约25%）与氧化型脑啡肽共洗脱，并且在阿片类相关物质的放射受体测定中也有信号。此外，这种物质对分离的豚鼠回肠和大鼠皮肤的血管通透性产生类似脑啡肽的作用。iENK的前体样蛋白与肾上腺前脑啡肽不同，因为用胰蛋白酶和羧肽酶B消化时它不会释放出iENK。由于胃蛋白酶可模拟肾素，这些结果表明血液中存在类似于肾素/血管紧张素系统的体系来生成具有生物活性的NT和ENK相关肽，同时也提出了是否可能发现其他神经肽以前体形式循环存在的问题。
