LIPOPROTEIN THAT SELECTIVELY INHIBITS TASTE NERVE RESPONSES TO BITTERSUBSTANCES

The development of a specific inhibitor for bitter taste has been wide ly required in the fields of taste physiology and pharmaceutical scien ces, but no inhibitor has been available. We found that lipoproteins, PA-LG composed of phosphatidic acid (PA) and p-lactoglobulin (LG) and PA-LA composed of PA and cu-lactalbumin (LA) reversibly suppressed the responses of the frog glossopharyngeal nerve to the bitter substances . The frog tongue was treated with PA-LG solution for 10 min and then stimulated by a stimulus dissolved in water. The responses to the bitt er substances such as quinine hydrochloride, papaverine hydrochloride, caffeine and L-leucine were completely suppressed by PA-LG, while tho se to the salt type bitter substances such as CsCl, MgCl2 and tetraeth ylammonium chloride were not suppressed. The responses to NaCl, galact ose, acetic acid and L-alanine were unchanged or only slightly increas ed. The results suggested that binding of PA-LG to the hydrophobic reg ion of the receptor membranes leads to suppression of the responses to the bitter substances. It was pointed out that PA-LG is useful not on ly for elucidating the receptor mechanisms of bitter substances, but a lso can be safely used to mask the bitter taste of foods and drugs, si nce PA, LG and LA are prepared from foods (soybean and milk).