Abstract
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 on the substrate ; 9.5 with tryptamine (TP) and 9.0 with serotonin (5HT). Apparent kinetic parameters were as follows ; the Km for TP was 45 μM and the Vmax 6.87 nmol product/mg protein/min, whereas the Km for 5HT was 190 μM and the Vmax 41.0 nmol product/mg protein/min. The Km for acetyl-CoA was 58 μM and the Vmax 6.88 nmol/mg/min with TP, whereas the Km 120 μM and the Vmax 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.
