Inhibition of brain choline acetyltransferase by tetraplatin

Tetraplatin inhibited choline acetyltransferase (CAT) from rat and bovine brain with I sub(50) values of 13.5 and 40 mu M, respectively. At 0.5 mM concentration, tetraplatin exhibited inhibition of the rat brain enzyme by 89%, whereas cisplatin yielded only 18% inhibition. With bovine CAT, tetraplatin showed noncompetitive inhibition with the substrate choline, K sub(m) 337 mu M, K sub(1) 29 mu M, V sub(max) 2.83 nmoles acetylcholine formed/min/mg protein, and competitive inhibition with the substrate acetyl-CoA, K sub(m) 21 mu M, K sub(1) 16 mu M, V sub(max) 3.85 nmoles acetylcholine formed/min/mg protein.