Influence of photoperiod on N-acetyltransferase activity and melatonin in the fiddler crab Uca pugilator.
Melatonin and N-acetyltransferase (NAT) activity were measured in the eyestalks of fiddler crabs acclimated to various photoperiods: constant light, a L:D 12:12 h photoperiod, or constant dark. Following acclimation, eyestalks were collected every 3 h over a 24-h period; they were assayed for melatonin with a radioimmunoassay and for NAT activity with a radioenzymatic assay. In constant light, melatonin levels increased at 1300 h, from 142 to 431 pg x mg(-1) eyestalk; NAT activity increased concurrently, from 97 to 203 pmol x h(-1) x mg(-1) eyestalk, and both remained elevated until 0400 h. In the L:D 12:12 h photoperiod, melatonin levels increased at 1300 h from 28 to 230 pg x mg(-1) eyestalk, and though NAT activity increased significantly, from 80 to 122 pmol x h(-1) x mg(-1) eyestalk, an even greater increase occurred at 0400 h, when melatonin levels were low. In constant dark, melatonin levels increased at 1600 h, from 22 to 196 pg x mg(-1) eyestalk, with a concurrent increase in NAT activity from 93 to 140 pmol x mg(-1) x h(-1) eyestalk. However, the second peak in melatonin (111 pg x mg(-1)), occurring at 0400 h, was out of phase with the second peak of NAT activity (113 pmol x mg(-1) x h(-1) eyestalk) which occurred at 0700 h. NAT may be a rate-limiting step in melatonin synthesis in fiddler crabs under some conditions (constant light and the 1300 h peak in constant dark); however, NAT activity correlates poorly with melatonin levels in a L:D 12:12 h photoperiod and in constant dark relative to the 0400 h melatonin peak.
Tilden
A R
AR
Biology Department, Colby College, 5720 Mayflower Hill, Waterville, Maine 04901, USA. artilden@colby.edu
Alt
J
J
Brummer
K
K
Groth
R
R
Herwig
K
K
Wilson
A
A
Wilson
S
S
D000818:Animals; D001191:Arylamine N-Acetyltransferase / Q000032:analysis / Q000378:metabolism* / Q000502:physiology; D003386:Brachyura / Q000201:enzymology* / Q000502:physiology; D005123:Eye / Q000201:enzymology / Q000378:metabolism; D008297:Male; D008550:Melatonin / Q000032:analysis / Q000096:biosynthesis*; D017440:Photoperiod; D011863:Radioimmunoassay
D001191:Arylamine N-Acetyltransferase; D008550:Melatonin