Nau R, Ballmann M, Conlon J M
Mol Cell Endocrinol. 1987 Jul;52(1-2):97-103. doi: 10.1016/0303-7207(87)90102-x.
Specific binding sites for 125I-labelled vasoactive intestinal polypeptide (VIP) (half-maximal inhibition at 1.5 +/- 0.2 nM VIP) were identified on dispersed porcine enterocytes. Radioactivity bound to the cell surface was internalized. At 37 degrees C, a steady state was achieved after 45 min with a ratio of internalized to cell surface-bound radioactivity of approximately 1:2 but at 10 degrees C, no radioactivity appeared intracellularly. Incubation of VIP with cells in the absence of inhibitors of proteolysis for as short a time as 30 s at 37 degrees C led to the formation of [des-His1]VIP by the action of amastatin- and bestatin-sensitive aminopeptidase(s). This metabolite was formed in the presence of sodium azide and when incubations were performed at 10 degrees C suggesting that internalization was not a prerequisite for degradation. As [des-His1]-VIP has only 1% of the bioactivity of VIP, formation of this metabolite will effectivily terminate the action of VIP in the epithelial layer of the intestine.
在分散的猪肠上皮细胞上鉴定出了125I标记的血管活性肠肽（VIP）的特异性结合位点（VIP浓度为1.5±0.2 nM时达到半数最大抑制）。与细胞表面结合的放射性物质被内化。在37℃时，45分钟后达到稳态，内化的放射性与细胞表面结合的放射性之比约为1:2，但在10℃时，细胞内未出现放射性。在37℃下，将VIP与细胞一起孵育，在不存在蛋白水解抑制剂的情况下，孵育时间短至30秒，就会通过氨肽酶抑制剂抑肽酶和苯丁抑制素敏感的氨肽酶作用形成[去组氨酸1]VIP。这种代谢产物在叠氮化钠存在的情况下形成，并且当在10℃下进行孵育时也会形成，这表明内化不是降解的先决条件。由于[去组氨酸1] - VIP仅具有VIP生物活性的1%，这种代谢产物的形成将有效地终止VIP在肠道上皮层中的作用。
