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Biomedical subjects

T Shinada

Publications and source records attributed to T Shinada.

At least 19 recordsLinked to original sources
PubMed1996

[Effects of the peripheral vision on visually induced vertigo].

Visually induced vertigo, or motion sickness, is thought to be mainly influenced by motion perception, not by shape perception. We examined this point by comparing the effect of the foveal vision on the visually induced vertigo with that of the peripheral vision. We set up three kinds of display conditions: Foveal vision (F), peripheral vision (P), and foveal + peripheral vision (F + P). Videotaped motion was presented on the display. The results showed that a drifting eye movement was larger after the experiment than before the experiment in the (P) and the (F + P) conditions, but not in the (F) condition. In addition, the mirror drawing was improved only in the (F) condition. Subjective ratings for the vertigo were higher in both the (P) and the (F + P) conditions than in the (F) condition. These results indicate that some visual units concerning low spatial frequencies participate in the visually induced vertigo.

Adult↗
PubMed1995

Biosynthesis of phytosiderophores, mugineic acids, associated with methionine cycling.

The biosynthesis of 2'-deoxymugineic acid, a key phytosiderophore, was examined in association with the putative methionine recycling pathway in the roots of wheat using labeling experiments and structural analysis. Feeding with D-[1-13C]ribose did not result in 13C enrichment of 2'-deoxymugineic acid, while D-[2-13C]ribose resulted in 13C enrichment at the C-4", -1, -4' positions, and D-[5-13C]ribose did in C-1', -4, and -1" positions of 2'-deoxymugineic acid, respectively. Furthermore, two isotope-labeled intermediates of the methionine recycling pathway, 5-[5-2H2]methylthioribose and 2-[1-13C]keto-4-methylthiobutyric acid, were synthesized, and their incorporation into 2'-deoxymugineic acids was investigated. Six deuterium atoms at the C-4, -1', and -1" positions of 2'-deoxymugineic acid were observed after feeding with 5-[5-2H2]methylthioribose. Feeding with 2-[1-13C]keto-4-methylthiobutyric acid yielded 2'-deoxymugineic acid enriched with 13C at the C-4', -1, and -4" positions. These results demonstrated for the first time that the biosynthesis of 2'-deoxymugineic acid is associated with the methionine recycling pathway. This association system functions to recycle methionine required for continued synthesis of mugineic acids in the roots of gramineous plants.

Azetidinecarboxylic Acid↗
PubMed1995

Interaction of tryptophan-182 with the retinal 9-methyl group in the L intermediate of bacteriorhodopsin.

An intense indole N-H stretching vibrational band at 3486 cm-1 in the difference Fourier transform infrared spectrum is one of the characteristic features of the L intermediate of bacteriorhodopsin [Maeda, Sasaki, Ohkita, Simpson, & Herzfeld (1992) Biochemistry 31, 12543]. This band is now assigned to tryptophan-182. The Trp182-->Phe (W182F) protein shows specific features in the difference spectrum in the visible region upon L formation, and exhibits great delay in the L-M conversion. Fourier transform infrared difference spectra further indicate that while the intensity of the C-methyl in-plane bending vibration at 1009 cm-1 is lost in the L intermediate of the wild type, its intensity remains high in the W182F protein. The intensity of the N-H stretching vibration upon L formation is diminished considerably in an artificial bacteriorhodopsin containing 9-desmethylretinal. It also exhibits delayed M formation. These results suggest that Trp182 interacts with the retinal side chain through the 9-methyl group, and thereby affects the L-to-M conversion.

Bacteriorhodopsins↗
PubMed1990

Synthesis of fluorine analogues of protoporphyrin potentially useful for diagnosis and therapy of tumors.

With the aim of obtaining a porphyrin derivative useful for diagnosis and therapy of cancer, fluorine analogues of protoporphyrin, in which the vinyl group(s) were replaced by difluorovinyl group(s), were synthesized by the reaction of the formylporphyrins with sodium chlorodifluoroacetate in the presence of triphenylphosphine. Some improvements in the reported procedures for the synthesis of formylporphyrins are also described. Preliminary results of biological tests of the products showed that 8(2),8(2)-difluoroprotoporphyrin accumulates to gastric cancer more selectively than other fluorine analogues and that 3(2),3(2),8(2),8(2)-tetrafluoroprotoporphyrin is taken up by rat hepatoma cells more readily than the others.

Animals↗
PubMed1978

Inhibitory effect of various gestagens upon the pregnenolone 3 beta-ol-dehydrogenase-delta 5-4-isomerase system in human corpora lutea of menstrual cycles.

The inhibitory effect of various gestagens upon the pregnenolone 3 beta-ol-dehydrogenase-delta5-4-isomerase system in 10,000 X g supernatants of human corpora lutea of the menstrual cycle has been investigated in in vitro experiments. The Km value for pregnenolone was 1.3 X 10(-6) M. All gestations reduced the rate of conversion of pregnenolone to progesterone. As compared with controls, average relative rates of reaction with additives were as follows: progesterone, 47%; 17-hydroxyprogesterone, 64% norethisterone, 33%; chlormadinone acetate, 47% medroxyprogesterone acetate, 53%; dydrogesterone, 62%; and allylestrenol, 74%. The data substantiate that natural or synthetic gestagens, at least in vitro, inhibit the conversion of pregnenolone to progesterone by human corpora lutea and that natural progesterone itself is a potent inhibitor which appears to acut noncompetitively (K1 =2.2 X 10(-5) M).

Adult↗
PubMed1975

The conversion of pregnenolone-7alpha-3H and progesterone-4-14C to estrogens by corpora lutea of menstrual cycles and pregnancy.

The metabolism of pregnenolone-7alpha-3H and progesterone-4-14C by human corpora lutea tissue of menstrual cycles and pregnancy was studied. In the incubations, equimolar mixtures of pregnenolone-7alpha-3H and progesterone-4-14C were used as substrates. Three corpora lutea of cycles were used as minced tissue. From those corpora lutea progesterone, 17-hydroxyprogesterone and androstenedione were formed, although no estrogens were formed. One corpus luteum of cycle and one corpus luteum of pregnancy were used as homogenated tissue, and those formed estrone and estradiol as well as the same three delta4-metabolites. The corpus luteum of cycle also formed testosterone. All metabolites including estrogens showed the lower 3H to 14C ratio than the starting ratio. 17-hydroxypregnenolone in only one corpus luteum, and no delta5-metabolites in the other four corpus luteum were identified. It is therefore proposed that the major pathway for estrogen formation in human corpus luteum is pregnenolone yields progesterone yields 17-hydroxyprogesterone yields androstenedione (or testosterone) yields estrone and estradiol.

Adult↗