Choline acetyltransferase activity in guinea-pig heart in vitro.

Ahstract Chi>line ;icctyltransfcrase (EC' 2.3.1.6) catallw, the following reversible rcaction: acetyl coen/jmc A + choline e acctylcholine + cocn7yme A. Enzyme activity in the atria and ventricles of guineapig h u r t wried indcpendcntly of the biochemically rclatcd carnitine acetyltransferasc (EC 2.3.1.7). Choline acctyltransfcrasc activity was greatest in right atrium. intermediate in right ventricle and left atrium and lowest iii left ventricle (4.05. 2.33 . 1.77 and 1.33 nmol minl g I, respcctively). Carnitine aoetyltransferase activity was greatest in the right and left ventricle and least in the right and left atria (8.86. 827, 3.18 and ?3X mniol min'g ~ I, respectively). Carnitine acetyltransferase activity was 800to 6000-fold greater than that of the choline acetyltransferase. depending on the chamber. Bromoacetylcholine inhibited acetylcholine. but not acetylcarnitine hiosynthe>ts in i : im>. Contrariwise. acetylcarnitine inhibited carnitine. but not cholinc acetyltransfcrasc. These results demonstrate the feasibility and specificity of measuring the differences in choline acetyltransferase activity in dialysed homogenates prepared from the four chambers of the heart.