PubMed Health⌕ Search

Biomedical subjects

T Taura

Publications and source records attributed to T Taura.

At least 37 records · Page 2Linked to original sources
PubMed1991

Does protein secretion activity vary during the cell cycle of Escherichia coli?

It is not known whether the activity of the Escherichia coli protein export system changes during the division cycle. To address and answer this question, we took two approaches. First, we pulse-labeled a random culture and size-fractionated the labeled cells in the presence of inhibitors of secretion. Second, we pulse-labeled synchronously growing cells at different phases in the cell cycle. In the latter experiment, we used a new method of synchronization in which a random culture was simply filtered through glass fiber filters. In both cases, the proportions of unprocessed precursor molecules were measured by immunoprecipitation and gel electrophoresis for some representative periplasmic and outer membrane proteins. Within the sensitivity limits of these methods, we could not detect any significant variation in the precursor labeling for cells of different ages. Thus, E. coli cells appear to secrete proteins continuously throughout the division cycle.

Autoradiography↗
PubMed1991

Inhibition in rat of development of in utero galactose-induced cataract by an aldose reductase inhibitor--a light microscopic study.

Aldose reductase inhibitors (ARIs) have been known to be effective in preventing galactose cataract by blocking the polyol pathway. Because the rat congenital galactose cataract is also induced by accumulated polyol, the effect of an ARI in the induction of congenital galactose cataract was investigated. Pregnant rats were placed on a 30% galactose diet. On fetal day 16, 17, 18 or 20, the fetal lenses were examined by light microscope. Lenses from newborn rats with mothers fed galactose diet until gestational day 16, 17, 18 or 20 and then given a galactose diet containing ARI were also examined. The fetal lenses obtained from galactose-fed mother rats on day 16 of gestation were morphologically similar to those of controls. On day 17, the experimental lenses displayed vacuolated areas. The lenses of newborn rats with mothers given an ARI diet after gestational day 16 showed no morphological changes, while a few small vacuoles were observed in the lens of rats with mothers given the ARI diet after day 17, 18 or 20 of gestation. ARI inhibited the rat congenital galactose cataract even when the drug was given to the mother rat during a late stage of pregnancy.

Aldehyde Reductase↗
PubMed1990

Characterization of cold-sensitive secY mutants of Escherichia coli.

Mutations which cause poor growth at a low temperature, which affect aspects of protein secretion, and which map in or around secY (prlA) were characterized. The prlA1012 mutant, previously shown to suppress a secA mutation, proved to have a wild-type secY gene, indicating that this mutation cannot be taken as genetic evidence for the secA-secY interaction. Two cold-sensitive mutants, the secY39 and secY40 mutants, which had been selected by their ability to enhance secA expression, contained single-amino-acid alterations in the same cytoplasmic domain of the SecY protein. Protein export in vivo was partially slowed down by the secY39 mutation at 37 to 39 degrees C, and the retardation was immediately and strikingly enhanced upon exposure to nonpermissive temperatures (15 to 23 degrees C). The rate of posttranslational translocation of the precursor to the OmpA protein (pro-OmpA protein) into wild-type membrane vesicles in vitro was only slightly affected by reaction temperatures ranging from 37 to 15 degrees C, and about 65% of OmpA was eventually sequestered at both temperatures. Membrane vesicles from the secY39 mutant were much less active in supporting pro-OmpA translocation even at 37 degrees C, at which about 20% sequestration was attained. At 15 degrees C, the activity of the mutant membrane decreased further. The rapid temperature response in vivo and the impaired in vitro translocation activity at low temperatures with the secY39 mutant support the notion that SecY, a membrane-embedded secretion factor, participates in protein translocation across the bacterial cytoplasmic membrane.

Bacterial Outer Membrane Proteins↗
PubMed1989

Transient shut off of Escherichia coli heat shock protein synthesis upon temperature shift down.

A moderate downward shift in growth temperature (37 to 30 degrees C in strain B/r and 37 to 24 degrees C in strain K-12) was found to depress markedly the synthesis of major heat shock proteins GroEL and DnaK in E. coli. The depression was transient and cancelled gradually to a new steady state level, taking 60-80 min. The synthesis of beta-galactosidase directed by transcription initiated at the groE promoter behaved similarly, suggesting that this regulation, termed "reverse heat shock response", occurs at the transcriptional level.

Bacterial Proteins↗
PubMed1988

Effect of sodium iodate injection on the development of galactose cataract in the rat.

The effect of sodium iodate injection on the development of galactose cataract in the rat was investigated clinically and biochemically. Galactose cataracts were induced in animals which had been injected with a single dose of sodium iodate and compared with those given a saline injection. The degeneration of retinal pigment epithelium was observed electron microscopically after sodium iodate injection. A slit lamp examination of the lens showed that, in animals injected with sodium iodate, galactose-associated lens alterations progressed faster, and mature cataract development was achieved earlier than in the saline-injected animals. Biochemical data which indicated a significantly higher concentration of Na+ and lower concentration of K+ in lenses of sodium iodate-injected animals confirmed the above clinical data. The level of galactitol was higher in lenses of sodium iodate-injected than those of saline-injected animals. Acceleration of the development of galactose cataract following sodium iodate injection is apparently due to the higher level of galactose entering the aqueous humor because of breakdown of blood-ocular barriers.

Animals↗
PubMed1985

Further observations on the effect of galactose on the development of X-ray-induced cataract in mice.

The effect of a 30% galactose diet on the progression of X-ray-induced cataract in mice was evaluated by following morphological changes as seen by light and transmission electron microscopy in different regions of the lens. Lens opacities as observed with the slit-lamp biomicroscope developed at a slower rate in galactose-fed animals than in those on a normal diet. The protective effect of galactose on X-ray cataract was seen whether galactose feeding was initiated either 1 week before or after exposure to X-ray. At 4 months after X-ray approximately 50% of galactose-fed animals had mature cataracts, compared to 100% in the control group. Similarly, at two weeks after exposure to X-ray, before any lens opacities were observed, morphological changes were more severe in the control group; cells in the meridional row were more disorganized in the control than in the galactose-fed groups. However, the progression of mature cataracts in the two galactose-fed groups were not significantly different. Since free radicals produced by X-ray are thought to be short-lived, the protective effect of galactose feeding after X-ray was unexpected, raising the possibility that some of the active species may be long-lasting. The nature of such radicals, if any, is unknown and remains to be investigated.

Animals↗
PubMed1983

Recovery of membrane potentials from diamide-induced depolarization in frog lens fibers.

Measurement of membrane potentials in isolated frog lens fibers was made by means of intracellular microelectrode techniques. The membrane potentials of lens fibers were depolarized to various degrees after exposure to diamide, an -SH inhibitor. When the degree of diamide-induced depolarization was less than 20 mV, the membrane potentials almost fully recovered to the control level within 12 h after immersion in a Ringer's solution containing dithiothreitol (DTT), a -SH protector. A similar tendency was also recognized in some lenses (57%) whose depolarization was 30 mV. When the degree of depolarization was 40 mV, the membrane potentials further depolarized in all cases tested in spite of treatment with DTT. From this study, it is considered that frog lens fibers could not recover their function if the damage was so severe as to produce a membrane depolarization of more 40 mV. Determination of ionic concentrations in lens fibers revealed a highly significant correlation between the degree of diamide-induced depolarization and changes in concentration ratio of Na+/K+.

Animals↗