Basic studies for the practical use of bitterness inhibitors: selective inhibition of bitterness by phospholipids.

PURPOSE: We examined the effects of phospholipids such as phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol (PI), and phosphatidic acid (PA) on human taste sensation to various substances. METHODS: The effects were evaluated psychophysically using paid volunteers. RESULTS: PA inhibited the bitterness of various substances dissolved in water without affecting sweetness, saltiness, and sourness, although its inhibitory activity was less than that of PA-LG. PI also showed inhibitory activity on bitterness, although its activity was less than PA. A soybean lecithin fraction containing high contents of PA and PI also demonstrated inhibitory activity on the bitterness of various substances. Both the incorporation of either PA or the lecithin fraction into granules containing quinine and the coating of the granules with PA or the fraction effectively inhibited the bitterness of quinine. CONCLUSIONS: The lecithin fraction is permitted for use as an additive to drugs and food and can be produced on an industrial scale. It is expected that the lecithin fraction will be used safely as a bitterness inhibitor for practical applications.

Quantitative histochemistry of the primate skin. III. Glyceraldehyde-3-phosphate dehydrogenase.

Glyceraldehyde-3-phosphate dehydrogenase activities were assayed with a fluorometric micromethod in various parts of the skin and its appendages. Enzyme activity was abundant, particularly in the epidermis and mucous membrane (4.2 to 11.3 moles/hr/kg dry wt.). The keratin layer of sole epidermis also contained a considerable amount of enzyme activity (2.6 moles/hr/kg dry wt.). A relatively low activity was found in the apocrine and sebaceous glands (1.8 to 3.6 moles/hr/kg dry wt.). The enzyme was influenced by various activators and inhibitors. The activators were 1-cysteine (200% increase), mercaptoethanol (+300%), EDTA (+300%), and the inhibitors, pCMB, Cu++ and Co++ (nearly 100% inhibition). Either arsenate or orthophosphate was an absolute requirement for the enzyme reaction. It is speculated that this dehydrogenase in skin and appendages may be a regulator of the Pasteur effect, hence of glycolysis, as it may be in muscle or in ascites tumor cells.

Quantitative histochemistry of the primate skin. I. Hexokinase.

A fluorometric micromethod, applicable to 0.5 to 5.0 µg skin samples, for the determination of hexokinase is described. The majority of the skin and appendages of the rhesus and stumptail macaques and the green monkey have hexokinase activity in the order of 250 to 500 mmoles/hr/kg dry weight. The ecerine sweat glands of the scalp have exceptionally high hexokinase activity, more than 1 mole/hr/kg dry weight. The possible physiological role of hexokinase in the skin as one of the key enzymes for glucose utilization is briefly discussed.

Enzymatic basis for active transport of Na+ in the sweat gland unit.

The presence of specific adenosine triphosphatase (ATPase) is demonstrated in the eccrine sweat gland units in the scalp of the rhesus monkey (0.2 moles/kg dry wt/hr) and in the sole of the pigtail macaque (1 mole/kg dry wt/hr). This ATPase is activated by combination of Na+ and K+, and this activation is counteracted by ouabain (10(-5) M) which is a specific inhibitor of Na+ transport. Thus, the occurrence of Na-K-ATPase in the sweat gland unit provides an enzymatic basis for participation of active transport of Na+ in the tissue.

Quantitative histochemistry of the primate skin.

Fructoaldolase activity in primate skin and appendages has been assayed with a highly sensitive fluorometric method. Epidermal fructoaldolase has characteristics similar to the fructoaldolases obtained from animal sources. The fructoaldolase activities of various skin structures are remarkably high; all glandular structures (except for apocrine sweat glands which have the highest activity of 2400 mmoles/hr/kg dry wt.) and active epidermal layers contain activities ranging from 1000 to 1600 mmoles/hr/kg dry weight. It is possible that these high fructoaldolase activities in skin and appendages reflect active glycolysis through the Embden-Meyerhof pathway.