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Y Ohsumi

Publications and source records attributed to Y Ohsumi.

At least 73 records · Page 4Linked to original sources
PubMed1995

Cloning of the gene encoding a putative serine/threonine protein kinase which enhances spermine uptake in Saccharomyces cerevisiae.

Polyamine uptake in Saccharomyces cerevisiae was modulated by extracellular magnesium; in a magnesium-limited medium, polyamine, especially spermine, was overaccumulated into the interior, whose level was then toxic for the growth of this organism (Maruyama, T., Masuda, N., Kakinuma, Y., and Igarashi K. (1994) Biochim. Biophys. Acta 1194, 289-295). Here we isolated a mutant (strain YTM22-8) whose growth was tolerant to spermine in magnesium-limited medium. This mutant was defective in polyamine uptake and did not overaccumulate spermine. From a yeast genome library we cloned a gene (POT1) which restored the spermine uptake of this mutant and the sensitivity of the growth to spermine. The nucleotide sequence of the POT1 gene indicated that it encodes a putative serine/threonine protein kinase and is located on chromosome XI. The results suggest that spermine uptake by this organism is probably regulated by phosphorylation and dephosphorylation.

Amino Acid Sequence↗
PubMed1995

Novel system for monitoring autophagy in the yeast Saccharomyces cerevisiae.

The yeast S. cerevisiae imports cytosolic components into the vacuole non-selectively by autophagy and degrades them by vacuolar hydrolases under nutrient starvation conditions. We developed a novel system for monitoring autophagy by constructing cells in which modified vacuolar alkaline phosphatase is expressed as an inactive precursor form in the cytosol. Under starvation conditions, the processing of the precursor to the mature form and phosphatase activity appeared gradually, and the mature form was located in the vacuole. Disruption of APG1, an essential gene for autophagy, resulted in no processing or phosphatase activity. These results indicate that the precursor form in the cytosol is transferred to the vacuole by autophagy and converted to the active form by vacuolar proteinases. Thus, autophagy could be determined easily and accurately by measuring the phosphatase activity.

Alkaline Phosphatase↗
PubMed1995

Human pulmonary vascular and venous compliances are reduced before and during left-sided heart failure.

Human pulmonary vascular and venous compliances were measured in 41 patients with or without left-sided heart failure. Two methods were used. Method 1 was based on analysis of pulmonary capillary wedge (PCW) pressure tracings according to Cv,PCW = (SF/100)(0.075PCW + 0.90)SV/[(v - d)PCW + 1], where Cv,PCW is compliance of pulmonary venous system, SF is systolic fraction of pulmonary venous flow [related to pulmonary capillary wedge pressure (PCW) as SF = 82 - 2.01PCW], (v - d)PCW is pulse pressure in PCW position, and SV is stroke volume. The (0.075PCW + 0.90) term equals k", i.e., systolic run-off ratio. Method 2 was used to measure to pulmonary vascular volume-pressure (V-P) relationship and pulmonary vascular compliance (Cvasc) and is based on measurement of pulmonary blood volume (PBV) and its increase with passive elevation of the legs to calculate Cvasc. Assuming the proportion of blood entering pulmonary venous system (in increase of PBV) during passive leg elevation to be 0.8, pulmonary venous compliance (Cv,PBV) was calculated as Cv,PBV = 0.8Cvasc. Cv,PCW correlated fairly closely with Cv,PBV (r = 0.81, coefficient of variation = 31%). This fair agreement between two independent methods suggests strongly that both methods may be valid, although other interpretations are possible. Cv,PCW, Cvasc, and Cv,PBV decreased going from New York Heart Association class I to classes II and III. When PBV was plotted vs. PCW, average V-P line for class II patients was flatter and shifted downward to the right compared with that for class I. This suggests pulmonary vasoconstriction as well as other factors. Average V-P line for class III patients is flatter but not displaced compared with that for class II. Another previously reported series of 50 patients, most of whom had ischemic heart disease, are included in this study.

Blood Pressure↗
PubMed1995

Analysis of the membrane structures involved in autophagy in yeast by freeze-replica method.

Under starvation conditions, the yeast S. cerevisiae sequesters its own cytoplasmic components by forming autophagosomes with double membrane in the cytoplasm. The autophagosome then fuses with the vacuolar membrane and delivers its own cytoplasmic components into the vacuole in the form of an autophagic body with a single membrane (Baba, M., Takeshige, K., Baba, N., and Ohsumi, Y. 1994. J. Cell Biol., 124: 903-913). We examined membrane structures involved in the autophagy induced by nitrogen-starvation by using freeze-replica method. The most conspicuous characteristic of the autophagic body is that the intramembrane particles were rarely detected on either the protoplasmic or exoplasmic face of its fracture membrane. This morphological feature of the fractured face was clearly different from other intracellular organelles. Next we examined the autophagosomal membrane. The inner membrane of autophagosome was also intramembrane particle-free, and its morphological feature was identical to the membrane of autophagic body. At the fusion site between autophagosome and vacuole we obtained direct evidence that two different membranes, the outer membrane of autophagosome and vacuolar membrane, became continuous by using freeze-etching technique. From these results we concluded that the autophagic body originated from the inner membrane of the autophagosome, and its membrane reflects an intrinsic feature of autophagosomal membrane. The outer membrane of autophagosome had only a few intramembrane particles and may be differentiated from the inner membrane. In cells under nitrogen-starvation condition, the density of intramembrane particles of vacuolar membrane decreased beyond that in control cells.

Autophagy↗
PubMed1995

[Sequential neuroimaging in a patient with delayed post-hypoxic leukoencephalopathy].

We described a patient with delayed cerebral demyelination following a post-operatively hypoxic encephalopathy. A 65-year-old man, with a history of exposure to the atomic bomb at Hiroshima in 1945, suffered from hypoxia, hypotension and respiratory acidosis and became unresponsive 10 hours after a laminectomy for lumbar disc herniation, in December 1993. Following an emergent resuscitation, the patient had gradually recovered and could walk 2 weeks later. Three weeks after the insult, however, the patient developed an apallic state with frontal lobe signs. Except an increased level of myelin basic protein in the CSF, there were no other abnormal laboratory findings. Brain CTs showed a leukoaraiosis. MRI one month post-operation, demonstrated extensive high signal intensity areas in the cerebral white matter on T2-weighted image, and a gadolinium-enhanced spotty lesion in the right globus pallidus on T1-weighted image. Three months after the operation, the high signal intensity on T2-weighted image became more intensive and extensive, while the enhanced spotty lesion in the globus pallidus disappeared. The corpus callosum and cerebellar white matter were spared throughout the observation. The SPECT using 123I-IMP showed a hypoperfusion in the frontal lobe at 1 month. Three months later, the hypoperfusion areas extended to the whole cerebral and cerebellar cortices, relatively less affected in the motor area and basal ganglia. The patient had improved slightly over the next few months. We speculate that subclinical vulnerability in the white matter secondary to exposure to the atomic bomb, in addition to the incomplete prolonged hypoxia, hypotension and acidosis, caused selective cerebral demyelination in this patient.

Aged↗
PubMed1995

[Warfarin therapy and chlorella].

Warfarin potassium (warfarin) is one of anticoagulants. Its anticoagulant effect is induced by inhibiting vitamin K in a complex manner. It is used effectively and safely in preventing cerebral embolism of cardiac origin, provided that thrombotest (TT) values is maintained from 10 to 20%. A 75-year-old man with atrial fibrillation and cardiomyopathy had cerebral embolism in the territory of the right middle cerebral artery. Warfarin therapy was started to prevent the recurrence of embolic stroke. TT values had been well controlled until intake of chlorella, but they rose above the therapeutic limit after its intake. There was no evidence of discontinuing warfarin, or taking drugs containing vitamin K or Natto. Chlorella is one of vitamin K-rich foods. Thus, it may inhibit the anticoagulant effect of warfarin.

Aged↗
PubMed1994

Saccharomyces cerevisiae MATa mutant cells defective in pointed projection formation in response to alpha-factor at high concentrations.

We have isolated Saccharomyces cerevisiae MATa mutant cells that do not form a pointed projection but elongate in response to alpha-factor at high concentrations. Complementation tests defined three genes, PPF1, PPF2, and PPF3 (for pointed projection formation), necessary for pointed projection formation. Allelism tests with genes known to be needed for projection formation revealed that PPF1 is identical to SPA2, while PPF2 and PPF3 are not allelic to SST2, STE2, SPA2, BEM1 or SLK1/SSP31/BCK1. The morphology of MATa ppf mutants treated with high concentrations of alpha-factor is similar to that of MATa PPF cells treated with alpha-factor at low concentrations. Quantitative mating tests showed that PPF2 and PPF3 are not essential for mating in either MATa or MAT alpha background. Monitoring of division arrest and expression of an alpha-factor-inducible gene revealed that mutations in the PPF genes do not affect the responses of MATa cells to low concentrations of alpha-factor. Unlike wild-type cells, the ppf mutants exhibited early recovery from alpha-factor-induced division arrest. Furthermore, vegetatively growing ppf3-1 cells are slightly defective in cell separation of mother and daughter cells and in selection of the correct bud sites in all cell types. These results indicate that PPF2 and PPF3 are involved in the response to alpha-factor at high concentrations and that PPF3 is also required for proper establishment of polarity in vegetative growth.

Cell Division↗
PubMed1994

Ultrastructural analysis of the autophagic process in yeast: detection of autophagosomes and their characterization.

Under nutrient-deficient conditions, the yeast S. cerevisiae sequesters its own cytoplasmic components into vacuoles in the form of "autophagic bodies" (Takeshige, K., M. Baba, S. Tsuboi, T. Noda, and Y. Ohsumi. 1992. J. Cell Biol. 119:301-311). Immunoelectron microscopy showed that two cytosolic marker enzymes, alcohol dehydrogenase and phosphoglycerate kinase, are present in the autophagic bodies at the same densities as in the cytosol, but are not present in vacuolar sap, suggesting that cytosolic enzymes are also taken up into the autophagic bodies. To understand this process, we performed morphological analyses by transmission and immunological electron microscopies using a freeze-substitution fixation method. Spherical structures completely enclosed in a double membrane were found near the vacuoles of protease-deficient mutant cells when the cells were shifted to nutrient-starvation media. Their size, membrane thickness, and contents of double membrane-structures corresponded well with those of autophagic bodies. Sometimes these double membrane structures were found to be in contact with the vacuolar membrane. Furthermore their outer membrane was occasionally seen to be continuous with the vacuolar membrane. Histochemical staining of carbohydrate strongly suggested that the structures with double membranes fused with the vacuoles. These results indicated that these structures are precursors of autophagic bodies, "autophagosomes" in yeast. All the data obtained suggested that the autophagic process in yeast is essentially similar to that of the lysosomal system in mammalian cells.

Alcohol Dehydrogenase↗
PubMed1994

[Comparison between 123I-BMIPP and 201TlCl myocardial imaging by circumferential profile analysis in patients with myocardial infarction--evaluation of effects of vascular reconstruction in patients with myocardial infarction].

We quantitatively evaluated the effects of vascular reconstruction according to the stage by 123I-BMIPP and 201TlCl using circumferential profile (CP) curve method in patients with myocardial infarction. (1) Comparison of the CP curves for the two nuclides in normal volunteers (n = 9) showed no difference in distribution. (2) In patient with myocardial infarction (n = 32) the severity score was evaluated using the CP curves obtained in the normal volunteers. Type B (marked decrease in 123I-BMIPP accumulation) accounted for 83% in the group in whom vascular reconstruction was performed in the acute stage (Group I) and 91% in the group in whom vascular reconstruction was performed in the chronic stage (Group II). On the other hand, type E (similar accumulation between the two nuclides) accounted for 79% in the group in whom vascular reconstruction was unsuccessful or was not performed (Group III). The severity score for each nuclide did not significantly differ among Group I, II and III. The 123I-BMIPP/201TlCl ratio was the highest in Group II, followed in order by Group I and Group III (p < 0.05). The assessment of the ratio of "severity scores" for both nuclides is considered to be useful for evaluation of the surviving myocardium, rather than the assessment of a single nuclide.

Adult↗
PubMed1993

Isolation and characterization of autophagy-defective mutants of Saccharomyces cerevisiae.

Autophagy in the yeast is similar to that in mammalian cells. A mutant designated as apg1 (autophagy) defective in accumulation of autophagic bodies in the vacuoles was isolated by selection using a light microscope from a mutagenized proteinase-deficient strain. In the apg1 strain, which has normal vacuolar proteinases, nitrogen starvation did not induce protein degradation. The apg1 mutant lost its viability faster than wild-type cells during nitrogen starvation. By using the loss of viability as a first screening test, 75 other apg mutants were selected. These apg mutants including apg1 fell into 15 complementation groups. Genetic analyses of representative apg mutants revealed that they all had single recessive chromosomal mutations. Strains with each apg mutation were defective in protein degradation in the vacuoles induced by nitrogen starvation and homozygous diploids for each apg mutation did not sporulate. These results on the apg mutants suggest that autophagy via autophagic bodies is indispensable for protein degradation in the vacuoles under starvation conditions, and that at least 15 APG genes are involved in autophagy in yeast.

Autophagy↗
PubMed1993

Density fluctuation during the cell cycle in the defective vacuolar morphology mutants of Saccharomyces cerevisiae.

The buoyant densities of the yeast cells of defective vacuolar morphology mutants were examined by equilibrium sedimentation centrifugation in a Percoll density gradient. These vacuoleless mutants also show density fluctuation as wild-type cells during the cell cycle. This suggests that morphological changes of the vacuole are not related to cyclic density fluctuation in Saccharomyces cerevisiae.

Cell Cycle↗
PubMed1993

[A case of apnea attacks due to an unilateral infarction in the right medulla oblongata].

We described a patient presenting with apnea attacks due to an unilateral small infarction in the right medulla oblongata. The patient was a 55-year-old man and was referred to our hospital because of severe headache and progressive left hemiparesis. Neurological examinations revealed left hemiparesis and the impairment of pain, touch, temperature and vibration sense in the left side of his body. Position sense was normal. Cranial nerves were intact including the trigeminal nerve. Ataxia was not noted. After an admission, the patient suffered from three episodes of apnea attack of sudden onset followed by cardiac arrest and convulsion. Magnetic resonance imaging demonstrated a clearly circumscribed small oblique lesion situated in the caudal lateral tegmental portion to the rostral ventromedial part of right medulla oblongata . The right vertebral artery was not visualized by magnetic resonance angiography. Serial computed tomography scans failed to identify this small lesion. We conclude that apnea attack in the present patient represents a central type apnea caused by the unilateral damage of the respiratory center in the medulla oblongata.

Apnea↗
PubMed1992

Genes for directing vacuolar morphogenesis in Saccharomyces cerevisiae. I. Isolation and characterization of two classes of vam mutants.

We identified nine VAM genes (for vacuolar morphology) by genetic analyses on mutants with defective vacuolar morphologies and assembly in the yeast Saccharomyces cerevisiae. The nine VAM genes were classified into two classes according to the mutant phenotypes. The class I vam mutants (vam1, vam5, vam8, and vam9) show a few small vesicles that are stained with histochemical markers for the vacuolar compartment. They also have defects in the maturation of vacuolar marker proteins, and their growth is hypersensitive to high concentrations of CaCl2 or a temperature of 37 degrees C. There are apparent genetic overlaps among the class I vam mutations and other mutations including cls, end, pep, and vps, which have been shown to be involved in the expression of the vacuolar functions. The class II vam mutants (vam2, vam3, vam4, vam6, and vam7) contain numerous small vesicles stained with the vacuolar histochemical markers and mature forms of the vacuolar proteins and do not show any apparent growth defects in the presence of CaCl2 or at 37 degrees C.

Blotting, Western↗
PubMed1992

Chloride transport of yeast vacuolar membrane vesicles: a study of in vitro vacuolar acidification.

Effects of various solutes on acidification inside the vacuolar membrane vesicles of the yeast Saccharomyces cerevisiae were examined. ATP-dependent acidification was stimulated by the presence of chloride salts. There was essentially no difference in the stimulatory effects of NaCl, KCl, LiCl, and choline chloride. The membrane potential across the vacuolar membrane was reduced by the presence of Cl- salts. Transport of 36Cl- is driven by the protonmotive force across the vacuolar membrane. Kinetic analyses have revealed that the stimulatory effect of Cl- on internal acidification depends on two distinct components. One shows linear dependency on chloride concentration and is inhibited by 4,4'-diisothiocyano-2,2'-stilbenedisulphonic acid (DIDS). The other exhibits saturable kinetics with an apparent Km for chloride of 15-20 mM. We conclude that the vacuolar membrane of yeast is equipped with Cl- transport systems contributing to the formation of a chemical gradient of protons across the vacuolar membrane by shunting the membrane potential generated by proton translocation.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗