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

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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 K_m for TP was 45 μM and the V_<max> 6.87 nmol product/mg protein/min, whereas the K_m for 5HT was 190 μM and the V_<max> 41.0 nmol product/mg protein/min. The K_m for acetyl-CoA was 58 μM and the V_<max> 6.88 nmol/mg/min with TP, whereas the K_m 120 μM 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.
日本応用動物昆虫学会の論文
1998-02-25