Characterization and kinetic analysis of indolamine N-acetyltransferase from the collaterial glands of the American cockroach, Periplaneta americana

Enzyme properties and kinetics of indolamine N-acetyltransferase (NAT) from female reproductive glands of Periplaneta americana were analyzed. The activity was restricted to the accessory glands and no activity was found in the ovary. The enzyme showed two pH optima, i.e., 6.0 and 9.0-9.5. The optimum at a higher pH range occurred at slightly different pHs depending an the substrate; 9.5 with tryptamine (TP) and 9.0 with serotonin (5HT). Apparent kinetic parameters were as follows; the K-m for TP was 45 mu M and the V-max 6.87 nmol product/mg protein/min, whereas the K-m for 5HT was 190 mu M and the V-max 41.0 nmol product/mg protein/min. The K-m for acetyl-CoA was 58 mu M and the V-max 6.88 nmol/mg/min with TP, whereas the K-m 120 mu M and the V-max 41.3 nmol/mg/min with 5HT. The kinetic analysis suggests that substrate binding proceeds according to a sequential Bi-Bi mechanism unlike the case of NAT from the cephalic ganglia.