MELATONIN PRODUCTION IN AN AEROBIC PHOTOSYNTHETIC BACTERIUM - AN EVOLUTIONARILY EARLY ASSOCIATION WITH DARKNESS

Melatonin was measured in a species of aerobic photosynthetic bacteria , Erythrobacter longus, grown in either constant light or constant dar k. A radioimmunoassay was used to quantify melatonin levels and thin-l ayer chromatography to confirm the identity of melatonin immunoactivit y. Melatonin levels were significantly higher (nearly 2.3-fold) in the dark-grown than in the light-grown samples. Also, the homogenates of the dark-grown bacteria retained melatonin-producing enzymatic activit y, whereas the light-grown homogenates did not; melatonin levels extra cted from the dark-grown homogenates increased with increasing extract ion time, reaching as high as 29.2 ng.mg-(1) protein at 120 min. Remov al of membrane fragments from homogenates did not influence melatonin levels in light-grown homogenate, but this procedure increased melaton in levels in dark-grown homogenate, indicating that at least some of t he enzymes in the pathway of melatonin production are not membrane-bou nd. This study is the second to demonstrate the presence of melatonin at the prokaryotic level, supporting the evidence that melatonin appea red very early in evolution. Its function in prokaryotes has not been determined, but may relate to its antioxidative actions.