The kinetic behavior of purified CDH had been investigated by steady-state initial velocity studies and inhibition studies with products. Variations in the concentration of one substrate led to changes in the K(m) and V(max) for the other substrate. The product betaine aldehyde was a noncompetitive inhibitor with respect to choline, whereas it competed with PMS. The results were consistent with a Bi-Bi Ping-Pong mechanism. 1-PC (1-pyrenebutyrylcholine bromide) and 9-AC (9-anthrolcholine bromide) behaved as mixed inhibitors, with K(i) values of 0.3 mM and 3.67 mM respectively.