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S Ohkuma

Publications and source records attributed to S Ohkuma.

At least 199 records · Page 11Linked to original sources
PubMed1984

Alteration of cerebral taurine biosynthesis in spontaneously hypertensive rats.

Cerebral taurine biosynthesis in a spontaneously hypertensive rat (SHR) has been studied. Cysteine sulfinic acid (CSA) and cysteic acid (CA), possible key intermediates in taurine biosynthesis, were found in the rat brain, whereas no cysteamine-cystamine was detected. In the brain of SHR, a statistically significant decrease in the contents of CSA, CA, and taurine was noted in the cerebellum, hypothalamus, and striatum as compared with normotensive Wistar Kyoto rats. Similarly, it was demonstrated that the activity of cysteine dioxygenase, the enzyme catalyzing cysteine to CSA, was attenuated significantly in the same brain areas of SHR. In contrast, no alteration in the activity of CSA decarboxylase, the enzyme converting CSA to hypotaurine or CA to taurine, was observed. A decline in the percent conversion of [14C]cysteine to [14C]taurine was found also in tissue homogenates from the cerebellum, hypothalamus, and striatum of SHR, indicating that the declines in taurine content may be due to an attenuation of taurine biosynthesis, possibly at the step involving cysteine dioxygenase.

Animals↗
PubMed1984

Roles of endogenous and exogenous taurine and glycine in the formation of conjugated bile acids: analyses using freshly isolated and primary cultured rat hepatocytes.

The regulatory roles of intracellular taurine and glycine, transported and biosynthesized in hepatocytes, on the formation of conjugated bile acids were studied using freshly isolated hepatocytes (fresh hepatocytes) and hepatocytes in primary culture (cultured hepatocytes). Transported taurine significantly increased the rate of taurocholic acid formation both in fresh hepatocytes and cultured hepatocytes. Similarly, the addition of cysteine and hypotaurine, which were metabolically converted to taurine in hepatocytes, facilitated the formation of taurocholic acid in these cells. On the other hand, exogenous glycine into the incubation medium had no effect on the formation of glycocholic acid both in fresh and cultured hepatocytes. In contrast, the addition of serine and threonine, which are metabolically converted to glycine in hepatocytes, significantly increased the formation of glycocholic acid in fresh hepatocytes, although little effect of the additions of serine and threonine on the formation of glycocholic acid was noted in the case of cultured hepatocytes. The present results indicate that the formation of taurine-conjugated bile acids in hepatocytes is maintained by both transported and intracellularly formed taurine in hepatocytes, while that of glycine-conjugated bile acids is regulated by glycine formed within hepatocytes, but not by transported glycine.

Animals↗
PubMed1984

Alteration of acetaldehyde metabolism in carbon tetrachloride-intoxicated rat liver: analysis using liver perfusion system.

The heptic metabolism of acetaldehyde in carbon tetrachloride (CCl4)-intoxicated rats was studied using a non-recirculating haemoglobin-free liver-perfusion system. Acetaldehyde uptake by the liver from acutely CCl4-treated animals (4.16 mmol/kg,i.p.) at 24 hr after the treatment was not significantly altered, whereas that by the liver from chronically CCl4-treated animals (2.08 mmol/kg,i.p., twice a week, for 8-12 weeks) was decreased by approximately 50% when it was determined in the presence of 0.01-5 mM acetaldehyde. In liver from rats chronically intoxicated with CCl4, the following important biochemical changes were observed: (1) The activity of low Km aldehyde dehydrogenase (ALDH) in hepatic mitochondria was decreased by approximately 75%. (2) The basal levels of the lactate/pyruvate (cytosolic [NADH]/[NAD+]) ratio as well as the beta-hydroxybutyrate/acetoacetate (mitochondrial [NADH]/[NAD+]) ratio were elevated by more than 2-fold. (3) Mitochondrial NADH oxidation was also reduced by approximately 35% of the control level. (4) The basal level of hepatic oxygen uptake was attenuated by approximately 50%, and the infusion of acetaldehyde (0.01-5.0 mM) caused a further decrease in the uptake. (5) The rate of ethanol production from acetaldehyde by the catalytic action of alcohol dehydrogenase was found to be unaltered when low concentrations of acetaldehyde (0.01-0.2 mM) were used, whereas a significant suppression of the rate of ethanol production was detected in the presence of high concentrations of acetaldehyde (0.6-5 mM).(ABSTRACT TRUNCATED AT 250 WORDS)

Acetaldehyde↗
PubMed1983

Characteristics of cholic acid uptake in primary cultured hepatocytes.

The characteristics of cholic acid uptake by primary cultured hepatocytes was studied. The cholic acid uptake below 10 degrees C was unsaturable, while that determined at 20 degrees and 37 degrees C showed a biphasic type, which suggested the presence of a saturable process. This saturable process was a temperature-dependent and carrier-mediated transport process with an activation energy of 36.1 Kcal/mol. The apparent Km and Vmax values at 37 degrees C were 57.1 microM and 0.566 nmoles/mg protein/min, respectively. The saturable process was inhibited by 2,4-dinitrophenol and ouabain, and reduced significantly in the absence of sodium, suggesting that this process is energy- and sodium-dependent. The cholic acid uptake mediated by the saturable process in the absence of sodium was, however, significantly larger than that mediated by the unsaturable process. These results suggest that the transport of cholic acid in primary cultured hepatocytes may consist of three different types: unsaturable, sodium and energy-dependent carrier-mediated, and sodium-independent and energy-dependent processes, respectively. The presence of a common transport carrier for cholic acid and its conjugates with taurine and glycine in primary cultured hepatocytes was also suggested.

Animals↗
PubMed1983

Effects of phospholipids on lysosomal acid lipase purified from rabbit liver.

The effects of phospholipids on lysosomal acid lipase purified from rabbit liver were studied. Non-ionic phospholipids such as phosphatidylethanolamine and phosphatidylcholine increased the enzyme activity. However, anionic phospholipids such as phosphatidylserine, phosphatidylinositol, and cardiolipin were ineffective. The acyl chain length and the degree of unsaturation of synthetic phospholipids were also related to the enzyme activity. Among a series of saturated phosphatidylcholines with different acyl chain lengths, 1,2-dipalmitoyl-sn-glycero-3-phosphorylcholine was the most effective. Among a series of unsaturated phosphatidylcholines, the enzyme activity increased in parallel with the number of double bonds. The role of lysosomal acid lipase in relation to phospholipids is discussed.

Animals↗
PubMed1983

Esterastin: a potent inhibitor of lysosomal acid lipase.

The effect of a fungal metabolite, esterastin, on lysosomal acid lipase purified from rabbit liver was studied. Esterastin inhibited the enzyme activity very strongly (IC50, about 80 nM). The inhibition of acid lipase by esterastin was competitive with respect to the substrate and the inhibition constant for esterastin was 90 nM. Esterastin was less inhibitory to other lipolytic enzymes, such as pancreatic lipase and carboxylesterase. Thus esterastin is a potent new inhibitor of lysosomal acid lipase.

Animals↗
PubMed1983

Electrogenic nature of lysosomal proton pump as revealed with a cyanine dye.

Studies were carried out on the electrogenicity of the lysosomal proton pump using dipropylthiadicarbocyanine iodide (diS-C3-(5] as a membrane potential probe. Pure lysosome preparations (tritosomes) quenched the fluorescence of diS-C3-(5). The quenching correlated well with the potassium ion diffusion potential (inside negative) generated by K+ with or without valinomycin. The quenching caused by lysosomes was reversed by lipophilic cations, tetraphenylarsonium (TPA) or triphenylmethylphosphonium (TPMP). Mg-ATP also reversed the quenching, which was inhibited by a protonophore, 3,5-di-tert-butyl-4-hydroxybenzylidene-malononitrile (SF-6847). The properties of the ATP-induced recovery of the quenching were exactly the same as those of ATP-induced acidification, as measured with fluorescein isothiocyanate-dextran (FD) (Ohkuma, S., et al. (1982) Proc. Natl. Acad. Sci. U.S. 79, 2758-2762) and acridine orange (Moriyama, Y., et al. (1982) J. Biochem. 92, 1333-1336), except replacement of the anion by an impermeable one enhanced ATP-induced recovery of quenching, but reduced ATP-induced acidification. Amines which dissipate delta pH across the lysosomal membrane also enhanced the Mg-ATP-induced fluorescence recovery. These results suggest that isolated lysosomes exhibit an inside negative membrane potential, especially in low K+ medium, mostly due to the K+-diffusion potential, and that the Mg-ATP-driven proton pump causes membrane depolarization (in the direction of inside positive). These possibilities were supported by results on the uptake of the radioactive membrane-permeant ions [3H]TPMP and [14C]SCN. The present results provide evidence for the electrogenic nature of the lysosomal proton pump.

Adenosine Triphosphate↗
PubMed1983

Two active forms of valyl-tRNA synthetase from Bacillus subtilis: alteration related to the early stages of sporulation.

Two enzymatically active forms, E-I and E-II, of valyl-tRNA synthetase [EC 6.1.1.9] from cells at various stages in the life cycle of Bacillus subtilis 168 LTT, germinated cells, vegetative cells (t-0.5), sporulating cells (t0, t1, t3, and t4), forespores and mature spores, were analyzed by hydroxyapatite column chromatography. The E-II activity was detected in the main fraction of valyl-tRNA synthetase during the life cycle of B. subtilis 168 LTT. The high activity of E-II at t0 decreased rapidly in the stationary and sporulating phases. On the other hand, the E-I activity increased in the early sporulating stage and was about twofold higher at t3 than at t0. After t3, this activity also decreased rapidly and was not detected in forespores and mature spores. The relative amount of E-I at t0 was 3.4% of the total valyl-tRNA synthetase activity eluted from the hydroxyapatite column, 12.9% at t1 and 29.2% at t3, but it was less than 10% at t4 and in germinated cells. The alteration in E-I and E-II activities was also observed in cells of B. subtilis NIG 1121 (spo+), W23 and 168W, but not in any asporogenous mutant strain studied. These results show that the alteration in the valyl-tRNA synthetase activity appears only during the early stages of sporulation and is closely related to the sporulation of B. subtilis.

Amino Acyl-tRNA Synthetases↗
PubMed1983

Lipid composition of low-density lysosomal membrane fraction prepared from atheromatous aorta of cholesterol-fed rabbits.

The lipid composition of low-density lysosomal membranes prepared from atheromatous aorta was analyzed. Results showed that the molar ratio of free cholesterol to phospholipids was 2.4, the phospholipids contained 49% sphingomyelin and 4% phosphatidylethanolamine and the phosphatidylcholine contained 22% polyunsaturated fatty acids. These values for the lipid composition are very different from those for normal biological membranes. The involvement of alteration of lysosomal membranes in accumulation of cholesterol ester in atherosclerosis is discussed.

Animals↗
PubMed1982

Uptake of cholic acid by freshly isolated rat hepatocytes: presence of a common carrier for bile acid transports.

The mechanism of the uptake of cholic acids and the interaction of various bile acids on the cholic acid uptake were investigated using isolated rat hepatocytes. The uptake consisted of unsaturable and saturable processes at 0 degrees C and 37 degrees C, respectively. The activation energy found for the saturable process was 26.1 Kcal/mol. In the saturable process the rate of cholic acid uptake followed Michaelis-Menten kinetics with Km: 67 microM and Vmax: 1.43 nmoles/ml protein/min. The uptake was significantly inhibited by 2,4-dinitrophenol, and replacement of extracellular Na+ by choline did not decrease the uptake. The uptake of cholic acid was competitively inhibited by deoxycholic acid, taurocholic acid, glycocholic acid, chenodeoxycholic acid, taurochenodeoxycholic acid and glycochenodeoxycholic acid. It is concluded from the above results that the cholic acid uptake in isolated hepatocytes is mainly mediated by an energy-dependent and sodium-independent carrier-mediated transport process.

2,4-Dinitrophenol↗
PubMed1982

Identification and characterization of a proton pump on lysosomes by fluorescein-isothiocyanate-dextran fluorescence.

Fluorescein isothiocyanate-conjugated dextran was introduced preferentially into hepatic lysosomes by intraperitoneal injection into rats. The pH in isolated lysosomes, measured by fluorescein fluorescence, was approximately 5 and gradually increased in KCl (to 7.0) at 25 degrees C. In the presence of Mg2+, ATP caused acidification of lysosomes that was reversed by the protonophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone. Mn2+, Co2+, and Fe2+ could replace Mg2+ but Ca2+ could not. Cu2+, Zn2+, and Cd2+ were inhibitory. A membrane-permeant anion, in practice chloride, was required for this acidification. ATP analogues, including 5'-adenylyl imidodiphosphate, could not be substituted for ATP. ATP-driven acidification was sensitive to N-ethylmaleimide and quercetin but insensitive to oligomycin, ouabain, and vanadate. There were some differences between "normal" lysosomes and tritosomes; the acidification was resistant to azide and N,N'-dicyclohexylcarbodiimide in normal lysosomes but sensitive to these reagents in tritosomes. These results provide evidence for the presence of an electrogenic proton pump driven by MgATP (H+-ATPase) on lysosomes.

Adenosine Triphosphate↗