Acetylation of Homocholine by Rat Brain: Subcellular Distribution of Acetylhomocholine and Studies on the Ability of Homocholine to Serve as Substrate for Choline Acetyltransferase In Situ and In Vitro
Acetylation of Homocholine by Rat Brain: Subcellular Distribution of Acetylhomocholine and Studies on the Ability of Homocholine to Serve as Substrate for Choline Acetyltransferase In Situ and In Vitro
复制标题
大鼠脑对高胆碱的乙酰化：乙酰高胆碱的亚细胞分布以及高胆碱作为胆碱乙酰转移酶底物的原位和体外能力研究
作者：
P. Boksa;B. Collier
摘要： 大鼠大脑皮层切片对高胆碱的原位乙酰化约为胆碱原位乙酰化的34%。大脑皮层切片合成的乙酰高胆碱与乙酰胆碱（ACh）分布在相同的亚细胞部分中，尽管乙酰高胆碱和ACh在无神经末梢储存和神经末梢结合储存之间的相对分布不同。小脑切片乙酰化高胆碱<10%，大脑皮质切片也是如此。在体外，胆碱乙酰转移酶（ChAT；EC 2.3.1.1.6）无论是从整个大鼠大脑中部分纯化，从裂解的突触体中溶解，还是以突触体膜相关形式，都不会以明显的速率乙酰化高胆碱。在碱性pH条件下，通过裂解的突触体制剂检测到可观的体外高胆碱乙酰化率。然而，对这种乙酰化的分析表明，它不是 ChAT 催化的结果，并且不太可能通过与原位高胆碱乙酰化相同的机制发生：乙酰化不受 ChAT 抑制剂抑制，并且在裂解的大脑皮质或小脑突触体制剂存在的情况下同样发生。结论是，高胆碱的原位乙酰化可能是由 ChAT 催化的，并且乙酰高胆碱随后储存在与 ACh 相同的亚细胞位点中；无法在体外检测 ChAT 催化的高胆碱乙酰化可能是酶分离过程中的人为因素。
Abstract: In situ acetylation of homocholine by slices of rat cerebral cortex was about 34% of the in situ acetylation of choline. Acetylhomocholine synthesized by the cerebral cortical slices was distributed in the same subcellular fractions as was acetylcholine (ACh), although the relative distribution of acetylhomocholine and ACh between nerve‐ending‐free and nerve‐ending‐bound stores was different. Cerebellar slices acetylated homocholine <10% as well as did cerebral cortical slices. In vitro, choline acetyltransferase (ChAT; EC 2.3.1.1.6) either partially purified from whole rat brain, solubilized from lysed synaptosomes, or in a synaptosomal membrane‐associated form, did not acetylate homocholine at an appreciable rate. Under conditions of alkaline pH, an appreciable in vitro rate of homocholine acetylation by preparations of lysed synaptosomes was detected. However, analysis of this acetylation showed it not to be the result of ChAT catalysis and unlikely to occur by the same mechanism as that responsible for acetylation of homocholine in situ: the acetylation was not inhibited by ChAT inhibitors and occurred equally in the presence of preparations of lysed cerebral cortical or cerebellar synaptosomes. It is concluded that in situ acetylation of homocholine is probably catalyzed by ChAT and that acetylhomocholine is subsequently stored in the same subcellular sites as is ACh; the inability to detect ChAT‐catalyzed acetylation of homocholine in vitro might arise as an artefact of the procedures employed in isolation of the enzyme.