VITAMINS

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A circadian oscillator in the chicken pineal cell regulates the diurnal oscillation of melatonin production. This circadian rhythm synchronizes to the environmental dark-light cycle through the intracellular photon-signal transduction machinery. One approach to the molecular events in the pineal circadian oscillator is to follow this photic input pathway toward the oscillator. To this end we identified a chicken pineal opsin, which binds 11-cis-retinal resulting in formation of a blue-light sensitive pigment with an absorption maximum at 470 nm. This photoreceptive molecule was named pinopsin. Immunohistochemical examination revealed the localization of pinopsin in the luminal membranes of all the follicles and in cilia-like structures and enlarged cilia with concentric lamellar arrays in the parafollicular zone. All the immunoreactive structures seemed to represent degenerated outer segments of photosensitive pinealocytes in the gland. The primary structure of cytoplasmic loops of pinopsin was similar to that of rhodopsin, raising a possibility that transducin (Gtαβγ) or Gt-like G-protein is involved in the pineal light-signal transduction process. We were able to clone a chicken pineal cDNA encoding the α-subunit of rod-type transducin (Gtlα), but the deduced amino acid sequence of the pineal Gtlα had a putative ADP-ribosylation site for pertussis toxin. Since the photic input pathway in the chicken pineal cell is insensitive to the toxin, it seems unlikely that this rod-type transducin mediates the pathway. Chicken pineal transducin may mediate the light-dependent acute inhibition of melatonin production.

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The most reliable assay method for niacin (a combined name of nicotinic acid + nicotinamide) in food is said to be microbial method at present. The authors investigated the assay method of niacin by HPLC in order to simplify the procedures and to save the assay time. 1) In order to determine niacin i food in the form of nicotinic acid, conditions for 2 fours with 0.5 M sulfuric acid was suitalble for the hydrolysis. 2) The limit of analysis of the present HPLC method under the above conditions was 0.1 mg/100 g food. The range recovery of nicotinic acid and nicotinamide spiked was between 100 and 104%, respectively. 3) Niacin contents in 35 kinds of food were assayed by HPLC and microbial methods. Values obtained by these two methods coincided well with each other.

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