Detection of melatonin, its precursors and related enzyme activities in rabbit lens

Citation
M. Abe et al., Detection of melatonin, its precursors and related enzyme activities in rabbit lens, EXP EYE RES, 68(2), 1999, pp. 255-262
Citations number
34
Language
INGLESE
art.tipo
Article
Categorie Soggetti
da verificare
Journal title
EXPERIMENTAL EYE RESEARCH
ISSN journal
0014-4835 → ACNP
Volume
68
Issue
2
Year of publication
1999
Pages
255 - 262
Database
ISI
SICI code
0014-4835(199902)68:2<255:DOMIPA>2.0.ZU;2-F
Abstract
Melatonin (N-acetyl-5-methoxytryptamine) was detected in extracts of albino rabbit lens using radioimmunoassay. Furthermore, melatonin precursors, try ptophan and serotonin (5-hydroxytryptamine), were found in the lens extract s by high-performance Liquid chromatography coupled with fluorometric detec tion. Also, activities of two melatonin-synthesizing enzymes, serotonin N-a cetyl-transferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT). were found in the lens. The apparent Michaelis constants (Km) for substrates of NAT in the lens were similar to those reported for the pineal gland, altho ugh the apparent Km values for substrates of HIOMT in the lens were 10-fold higher than those in the pineal gland, When the rabbits were entrained to a 14-hr light: 10-hr dark cycle. melatonin levels and NAT activity in the l ens showed significant day/night changes with high levels during the dark p eriod, but HIOMT activity did not show these changes. These findings strong ly suggest that the rabbit lens may synthesize melatonin from serotonin by the sequential action of NAT and HIOMT, and that the melatonin synthesis ma y fluctuate in a diurnal and/or circadian manner. (C) 1999 Academic Press.