Tyramine and β-phenylethylamine,from fermented food products,as agonists for the human trace amine-associated receptor 1 (hTAAR1) in the stomach

The aromatic amines tyramine and β-phenylethylamine are abundant in fermented foods. Recently, a family of human trace amine-associated receptors (hTAARs) was discovered that responds to these compounds. This study examined the expression of hTAAR genes in five human organs. Among them, the stomach expressed hTAAR1 and hTAAR9. Interestingly, more hTAAR1 was expressed in the pylorus than in the other stomach regions. The CRE-SEAP reporter assay revealed that only hTAAR1 functioned as a G_s-coupled receptor in response to tyramine and β-phenylethylamine stimulation. The β-phenylethylamine-mediated hTAAR1 activity could be potentiated using 3-isobutyl-1-methylxanthine. These data suggest that tyramine and β-phenylethylamine in fermented foods act at hTAAR1 as agonists in the pylorus of stomach.     

Symbiotic <Emphasis Type="Italic">Chlorella variabilis</Emphasis> strain, 1 N,can influence the digestive process in the host <Emphasis Type="Italic">Paramecium bursaria</Emphasis> during early infection

The association between the ciliate Paramecium bursaria and symbiotic Chlorella spp. is mutually beneficial. However, this relationship is facultative mutualism because both the host and the symbiotic algae can grow by themselves. This association is easily re-established by mixing the two species together. Following algal mixing, some algae become enclosed in the digestive vacuole membrane of the paramecia to which both acidosomes and lysosomes fuse. To establish endosymbiosis, some algae acquire temporal resistance to the host lysosomal enzymes in the digestive vacuoles. We examined whether the algae influence the differentiation of the host digestive process using LysoSensor staining to evaluate the acidification of the digestive vacuoles. Furthermore, to assess lysosomal fusion with the digestive vacuole, Gomori’s staining was conducted. Acidification and lysosomal fusion occurred later in digestive vacuoles containing living algae than in those containing boiled algae or latex spheres. This phenomenon was observed when the living algae were maintained under a constant light condition. These results suggest that the algae release some unknown factor in response to light exposure, and the factor may be associated with the alteration of the host digestive process, indicating that the living algae can influence the host digestive processes during early algal infection.     

Inhibition of lipoxygenase-dependent lipid peroxidation by quercetin: Mechanism of antioxidative function

Quercetin inhibited soybean lipoxygenase-1-dependent linoleic acid peroxidation. Two to three μM quercetin was required for 50% inhibition. During the inhibition, quercetin was oxidized. The oxidation was observed as an absorbance decrease at about 380 nm and an absorbance increase at about 335 nm. Inhibition of linoleic acid peroxidation by quercetin seems to be due to reduction by the reagent of the linoleic acid radical formed as an intermediate during lipoxygenation. Quercetin oxidation was suppressed by ascorbate under conditions when ascorbate did not affect lipoxygenase-dependent linoleic acid peroxidation. The results suggest that ascorbate can reduce the quercetin oxidized by the linoleic acid radical back to quercetin. Based on the results, the significance of a redox reaction between oxidized quercetin and ascorbate is discussed.     

Oxidation-reduction reactions between electron transfer components and hydrogen peroxide in photosystem II of chloroplasts

The light-induced oxygen evolution, photoreduction of 2,6-dichlorophenolindophenol (DPIP) and carotenoid photobleaching induced by carbonylcyanide m-chlorophenylhydrazone (CCCP) were investigated withspinach chloroplast fragments in the presence of H₂O₂. Oxygenevolution in the presence of H₂O₂ was not inhibited by CCCPand was only partially inhibited by 5 µM 3-(3,4-dichlorophenyl)-1,1-dimethylurea(DCMU) which completely inhibited the Hill reaction with DPIP.The degree of inhibition by DCMU was decreased by a simultaneousaddition of CCCP. Carotenoid photobleaching in the presenceof CCCP was stimulated by H₂O₂. The CCCP-induced carotenoidphotobleaching was completely inhibited by DCMU. However, itwas only partially inhibited by DCMU in the presence of H₂O₂.These data indicate that H₂O₂ donates electrons at a site betweenthe CCCP-sensitive site and the reaction center of photosystemII and is reduced at a site between the DCMU-blocked site andthe reaction center of photosystem II. ¹Present address: Department of Biology, Kyushu Dental College,Kitakyushu 803, Japan. (Received June 20, 1974; )     

Regulation of Peroxidase-Dependent Oxidation of Phenolics in the Apoplast of Spinach Leaves by Ascorbate

The aqueous phase of the cell walls inside leaves (apoplast)of spinach contained ascorbate (AA) and dehydroascorbate (DHA).Ratios of AA to AA plus DHA were between 0.4 and 0.9, whereasthose inside leaves were higher than 0.9. The amounts of AAplus DHA in the apoplast were between 15 and 60 nmol (g fr wt)^–1of leaves. If the volume of the apoplast is about 10% of totalvolume of leaf cells, the concentrations of AA plus DHA werebetween 0.15 and 0.6 mM. Apoplastic AA was oxidized by hydrogenperoxide, and the oxidation was stimulated by phenolics suchas caffeic acid or ferulic acid by a factor of 10, suggestingthe presence in apoplast of peroxidases which are differentfrom AA peroxidase. The stimulation was due to the oxidationof AA by the primary oxidation products of phenolics with apoplasticperoxidase. Based on the data, the physiological significanceof the occurrence of AA in the apoplast is discussed in relationto the regulation of the apoplastic oxidation of phenolics. (Received January 8, 1992; Accepted February 28, 1992)     

Effects of electron donor and acceptors, electron transfer mediators, and superoxide dismutase on lipid peroxidation in illuminated chloroplast fragments

Effects of artificial electron donor and acceptors, electrontransfer mediators, and superoxide dismutase on lipid peroxidationin illuminated chloroplast fragments were studied. An indicator of lipid peroxidation, malondialdehyde (MDA) formation,was stimulated by 3-(3,4-dichlorophenyl)-l,l-dimethylurea (DCMU).The DCMU stimulated MDA formation was inhibited about 90% byreduced 2,6-dichloroindophenol (DCIP). In photosystem I-enrichedparticles, MDA formation was larger than that in normal chloroplastfragments on the chlorophyll basis. Benzyl viologen and ferredoxinstimulated DMA formation. Superoxide dismutase inhibited MDAformation strongly in the presence of benzyl viologen and weaklyin its absence; the enzyme sometimes stimulated MDA formationin the presence of ferredoxin. Carbonylcyanide m-chlorophenylhydrazone(CCCP) stimulated MDA formation and maximal stimulation wasattained at about 20 µM CCCP.Phenazine methosulfate, DCIPand benzoquinone inhibited MDA formation in the presence andabsence of CCCP. From the above results, we confirmed our previous conclusionthat most of the singlet molecular oxygen formed in illuminatedchloroplasts is generated by electron transfer from O_2^–to oxidized electron transfer components located on the oxidizingsides of photosystems I and II. (Received September 3, 1975; )     

Suppression of Carotenoid Photobleaching by Kaempferol in Isolated Chloroplasts

The effects of kaempferol on carotenoid photobleaching wereexamined using chloroplasts poisoned by carbonylcyanide m-chlorophenylhydrazone(CCCP). Kaempferol suppressed carotenoid photobleaching withoutaffecting electron transfer reactions. Half-maximal suppressionwas observed at about 10 µM. Kaempferol was photooxidizedby CCCP-poisoned chloroplasts, as observed by its bleachingat 380 nm. Ascorbate inhibited the oxidation of kaempferol.Under anaerobic conditions, kaempferol did not affect the photobleachingof carotenoid. Other fiavonols, quercetin and its glycosides,also suppressed the carotenoid photobleaching. The results suggestthat flavonols act as antioxidants in illuminated chloroplastsunder aerobic conditions. (Received February 22, 1982; Accepted May 14, 1982)     

Hydroxycinnamic acid esters enhance peroxidase-dependent oxidation of 3, 4-dihydroxyphenylalanine. differences in the enhancement among the esters

Horseradish peroxidase (HRP)-dependent oxidation of 3, 4-dihydroxyphenylalanine (dopa) was studied to elucidate the mechanism of its oxidation. The oxidation of dopa was enhanced by hydroxycinnamic acid esters and dopa supressed HRP-dependent oxidation of the esters. These results indicate that phenoxyl radicals of hydroxycinnamic acid esters that are formed at first, can oxidize dopa. Among hydroxycinnamic acid esters used, affinity of the phenoxyl radicals for dopa was in order 4-coumaric>caffeic>ferulic acid ester radicals.