The binding of substance P (SP) to synaptic vesicles from rat brain was studied by use of the 125I-Tyr8-analogue of SP. 2. The pH dependence of the binding of both peptides to the lipid extractable fraction of synaptic vesicles was shown to be comparable. 3. The binding of 125I-Tyr8-SP shows a rate constant of association (k1 = 6.6 x 10(6) M-1 S-1), a rate constant of dissociation (k-1 = 6.4 x 10(-4) S-1) and gives a KD of 1 x 10(-10) M. Kd derived from equilibrium studies was 3.2 x 10(-10) M. 4. The binding of 125I-Tyr8-SP to lipids of synaptic vesicles was shown to be reversible, saturable and highly specific. 5. The kinetic data suggest one population of binding sites with a maximal number of 0.8 pmol per mg protein of the synaptic vesicle preparation. 6. Unlabeled SP and the (2--11)-, (3--11)- and (4--11)-analogues of SP inhibit the binding of 125I-Tyr8-SP in a decreasing order in a competitive way when added in excess. Tyr8-SP and eledoisin did not interfere with the binding of 125I-Tyr8-SP whereas uperolein and neurotensin caused a partial inhibition. Physalaemin and D-Ala2-D-Met5-enkephalin enhance the binding of 125I-Tyr8-SP in a cooperative way.
摘要
利用P物质（SP）的125I-Tyr8类似物研究了其与大鼠脑突触小泡的结合。2. 两种肽与突触小泡脂质可提取物部分的结合对pH的依赖性显示出相似性。3. 125I-Tyr8-SP的结合显示出缔合速率常数（k1 = 6.6 x 10(6) M-1 S-1）、解离速率常数（k-1 = 6.4 x 10(-4) S-1），KD为1 x 10(-10) M。来自平衡研究的Kd为3.2 x 10(-10) M。4. 125I-Tyr8-SP与突触小泡脂质的结合显示为可逆、饱和且高度特异性的。5. 动力学数据表明存在一类结合位点，每毫克突触小泡制剂蛋白的最大数量为0.8皮摩尔。6. 未标记的SP以及SP的(2--11)-、(3--11)-和(4--11)-类似物在过量添加时以竞争方式按递减顺序抑制125I-Tyr8-SP的结合。Tyr8-SP和eledoisin不干扰125I-Tyr8-SP的结合，而uperolein和神经降压素引起部分抑制。蛙皮素和D-丙氨酸2-D-蛋氨酸5-脑啡肽以协同方式增强125I-Tyr8-SP的结合。
