Spielholz N I, Van der Kloot W G
J Cell Biol. 1973 Nov;59(2 Pt 1):407-20. doi: 10.1083/jcb.59.2.407.
Cholinesterase (ChE) activity is present in crustacean muscle extracts. However, since acetylcholine (ACh) is not a neuromuscular transmitter in these animals, the role and exact localization of ChE was unknown. The histochemical localization of the enzyme was studied in whole muscle and in the sarcoplasmic reticulum fraction of the extract, 50-microm frozen sections of glutaraldehyde-fixed crayfish tail flexor muscle were incubated with acetylthiocholine (ATC) as substrate, and examined under the electron microscope. After some modifications in published techniques, dense deposits were found associated with the sarcolemma, sarcolemmal invaginations, and transverse tubules. No deposits were found in 10(-4) M eserine, or if butyrylthiocholine (BTC) was substituted for ATC. The vesicles in the sarcoplasmic reticulum fraction which demonstrate the activity must represent minced bits of these membranes. Using a spectrophotometric method, the kinetics of the crustacean muscle enzyme was compared to the acetylcholinesterase (AChE) on mammalian red blood cells and in the lobster ventral nerve cord. Surprisingly, and contrary to previous reports, the crustacean muscle enzyme did not demonstrate substrate inhibition. While a number of similarities to AChE were found, this lack of substrate inhibition makes questionable an unequivocal similarity with classical AChE.
甲壳类动物肌肉提取物中存在胆碱酯酶（ChE）活性。然而，由于乙酰胆碱（ACh）并非这些动物的神经肌肉递质，ChE的作用及确切定位尚不清楚。在整个肌肉以及提取物的肌浆网部分研究了该酶的组织化学定位，将戊二醛固定的小龙虾尾部屈肌的50微米冰冻切片与乙酰硫代胆碱（ATC）作为底物一起孵育，并在电子显微镜下检查。在对已发表技术进行一些修改后，发现致密沉积物与肌膜、肌膜内陷和横小管有关。在10（-4）M毒扁豆碱中未发现沉积物，或者用丁酰硫代胆碱（BTC）替代ATC时也未发现沉积物。肌浆网部分中显示活性的囊泡必定代表这些膜的碎块。使用分光光度法，将甲壳类动物肌肉酶的动力学与哺乳动物红细胞和龙虾腹神经索中的乙酰胆碱酯酶（AChE）进行了比较。令人惊讶的是，与先前的报道相反，甲壳类动物肌肉酶未表现出底物抑制作用。虽然发现了与AChE的许多相似之处，但这种缺乏底物抑制作用使得与经典AChE的明确相似性受到质疑。
