Burbach J P, De Kloet E R, De Wied D
Brain Res. 1980 Dec 8;202(2):401-14. doi: 10.1016/0006-8993(80)90151-1.
The enzymatic conversion of oxytocin by brain peptidases has been studied. Oxytocin was incubated with synaptosomal plasma membranes (SPM) isolated from the rat brain. Qualitative studies using a microdansylation technique revealed two types of oxytocin converting peptidases, e.g. aminopeptidase and C-terminal cleaving peptidase activities. Both enzyme activities were quantitated using [14C]oxytocin labeled at either the tyrosine-2 or the glycinamide-9 residue. Radiolabeled products were separated by high-voltage paper electrophoresis or high-pressure liquid chromatography. The aminopeptidase activity was optimally active at pH 6.9 with a Michaelis constant (Km) of 6.1 x 10(-5) M. The pH optimum of the C-terminal cleaving peptidase activity was pH 6.0 with Km = 1.3 x 10(-5) M. Subcellularly, highest amino-peptidase activities were associated with SPM, synaptosomal and microsomal preparations, while the C-terminal cleaving peptidase prevailed in the cytosol and mitochondrial fractions. The regional distribution of both peptidases showed differences between several brain areas and indicated the medial basal hypothalamus as a locus of high oxytocin biotransformation. In the course of this investigation an oxytocin fragment of unknown structure was detected in the digests and its accumulation was studied together with the determination of peptidase activities. It is suggested that the SPM-associated peptidases may have a role in the modulation of oxytocin action in the brain.
已经对脑肽酶催化催产素的转化进行了研究。将催产素与从大鼠脑中分离出的突触体细胞膜（SPM）一起孵育。使用微量丹磺酰化技术进行的定性研究揭示了两种类型的催产素转化肽酶，即氨肽酶和C末端裂解肽酶活性。使用在酪氨酸-2或甘氨酰胺-9残基处标记的[14C]催产素对这两种酶活性进行定量。通过高压纸电泳或高压液相色谱分离放射性标记产物。氨肽酶活性在pH 6.9时活性最佳，米氏常数（Km）为6.1×10（-5）M。C末端裂解肽酶活性的最适pH为6.0，Km = 1.3×10（-5）M。在亚细胞水平上，最高的氨肽酶活性与SPM、突触体和微粒体制剂相关，而C末端裂解肽酶在胞质溶胶和线粒体部分中占优势。两种肽酶的区域分布在几个脑区之间存在差异，并表明内侧基底下丘脑是催产素生物转化的高活性位点。在这项研究过程中，在消化物中检测到一种结构未知的催产素片段，并在测定肽酶活性的同时对其积累进行了研究。有人提出，与SPM相关的肽酶可能在调节脑中催产素的作用方面发挥作用。
