B. Withyachumnarnkul et al., N-ACETYLTRANSFERASE, HYDROXYINDOLE-O-METHYLTRANSFERASE AND MELATONIN IN THE OPTIC LOBES OF THE GIANT TIGER SHRIMP PENAEUS-MONODON, Journal of pineal research, 18(4), 1995, pp. 217-221
The activities of the enzymes N-acetyltransferase (NAT) and hydroxyind
ole-O-methyltransferase (HIOMT) and the hormone melatonin were studied
in the optic lobe of the subadult giant tiger shrimp Penaeus monodon.
Compared with the level in other species, a relatively high level of
NAT activity that was temperature- and pH-dependent were observed. The
NAT enzyme had a relatively high maximum velocity (Vmax, 100 pmol/hr/
mu g protein) and low Michaelis constant (Km, 22 mu M), when tryptamin
e is used as substrate. Tn contrast to the high level of NAT activity,
HIOMT activity and melatonin levels were low in the optic lobe of the
giant tiger shrimp. Sex differences in the levels of NAT activity and
melatonin, which are observed in a freshwater species Macrobrachium r
osenbergii, were not noticeable in the saltwater species P. monodon, a
t least not when they were in their subadult stage.