Arylalkylamine N-acetyltransferase activity parallel to work types and their temporal shift suggests its involvement in polyethism regulation in Apis mellifera workers

Arylalkylamine N-acetyltransferase (AANAT) is a large family of enzymes that catalyze the acetyl-CoA-dependent acetylation of an amine or arylalkylamine. Some AANATs, such as serotonin N-acetyltransferase, in vertebrates are photosensitive and mediate circadian regulation of melatonin and are involved in important biological processes. We analyzed AANAT activity of the honey bee, Apis mellifera, and found a relationship to the polyethism of workers. Crude AANAT solutions from isolated heads had optimum pHs at 8.0 (a minor peak) and 10.0 (a major peak). The Lineweaver–Burk (or double reciprocal plot) and the secondary plot (derived from the Lineweaver–Burk), gave the K_m for tryptamine (substrate) as 2.65 µM, and the V_max of 53.2 nmol/mg protein/min. The apparent K_m and V_max for acetyl-CoA was 20.5 µM and 6.98 nmol/mg protein/min, respectively. AANAT activity showed a correlation with the age of workers. The highest AANAT activity was found in 42-day old workers and the lowest in 3-day old workers. The highest AANAT activity was found in foragers and the lowest in hive-making workers. Two AANAT genes were retrieved from the A. mellifera genome. Putative cis-acting elements involved in circadian regulation, metamorphic and caste related expression were explored within both genes to discuss potential implication of the circadian clock in regulation of polyethism. The results suggest that AANATs are associated with regulation of social behavior in honey bees in circadian manners, in both foraging rhythms and polyethism.