Goodman D R, Adatsi F K, Harbison R D
Chem Biol Interact. 1984 Apr;49(1-2):39-53. doi: 10.1016/0009-2797(84)90051-6.
Detection of choline acetyltransferase (ChAc) in a number of non-neuronal tissues has been extremely overestimated. There are two major types of errors encountered. Type 1 error occurs when endogenous substrates (e.g. L-carnitine) are acetylated by acetyltransferase enzymes (e.g. carnitine acetyltransferase ( CarAc ) ) yielding an acetylated product mistaken for acetylcholine (AcCh). In the past, human sperm and human seminal plasma putative ChAc activity has been extremely overestimated due to Type 1 error. This study demonstrates (1) an endogenous acetyltransferase and substrate activity in human sperm and human seminal plasma forming an acetylated product that is not AcCh but probably acetylcarnitine ( AcCar ); (2) that the addition of 5 mM choline substrate does not significantly increase acetyltransferase activity; (3) that boiled seminal plasma contains an endogenous acetyltransferase substrate which is not choline, but probably L-carnitine. Type 2 error occurs when endogenous carnitine acetyltransferase synthesizes true AcCh, resulting in mistaken evidence for ChAc. This is demonstrated by the fact that the choline substrate Km-value for the neuronal or true ChAc from mouse brain is 0.73 +/- 0.06 mM while the Km-value of choline substrate for purified CarAc from pigeon breast muscle is 108 +/- 4 mM. Type 2 error has occurred for the estimation of putative ChAc in rat heart. The rat heart ChAc was measured in previous studies utilizing a concentration of 30 mM choline substrate. While saturation of neuronal ChAc is observed at 2-5 mM choline, saturation of the rat heart CarAc enzyme is not reached until over 800 mM. Purified CarAc significantly synthesizes AcCh at 30 mM choline. Thus, putative ChAc has been greatly overestimated in the scientific literature for mammalian sperm, human seminal plasma and rat heart.
许多非神经元组织中胆碱乙酰转移酶（ChAc）的检测被严重高估。主要存在两种错误类型。1型错误发生在内源性底物（如L-肉碱）被乙酰转移酶（如肉碱乙酰转移酶（CarAc））乙酰化，产生被误认为是乙酰胆碱（AcCh）的乙酰化产物时。过去，由于1型错误，人类精子和人类精浆中假定的ChAc活性被严重高估。本研究表明：（1）人类精子和人类精浆中存在内源性乙酰转移酶和底物活性，形成的乙酰化产物不是AcCh，而是可能的乙酰肉碱（AcCar）；（2）添加5 mM胆碱底物不会显著增加乙酰转移酶活性；（3）煮沸的精浆含有一种内源性乙酰转移酶底物，它不是胆碱，而是可能的L-肉碱。2型错误发生在内源性肉碱乙酰转移酶合成真正的AcCh时，从而导致ChAc的错误证据。这一点可通过以下事实得到证明：小鼠脑神经元或真正的ChAc的胆碱底物Km值为0.73±0.06 mM，而鸽胸肌纯化的CarAc的胆碱底物Km值为108±4 mM。在大鼠心脏中假定的ChAc估计中出现了2型错误。在先前的研究中，使用30 mM胆碱底物浓度测量大鼠心脏ChAc。虽然在2-5 mM胆碱时观察到神经元ChAc饱和，但直到超过800 mM时大鼠心脏CarAc酶才达到饱和。纯化的CarAc在30 mM胆碱时能显著合成AcCh。因此，在科学文献中，哺乳动物精子、人类精浆和大鼠心脏中假定的ChAc被大大高估了。
