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Biomedical subjects

S Ohki

Publications and source records attributed to S Ohki.

At least 145 records · Page 8Linked to original sources
PubMed1979

Divalent cation-induced interaction of phospholipid vesicle and monolayer membranes.

The effects of phospholipid vesicles and divalent cations in the subphase solution on the surface tension of phospholipid monolayer membranes were studied in order to elucidate the nature of the divalent cation-induced vesicle membrane interaction. The monolayers were formed at the air/water interface. Various concentrations of unilamellar phospholipid (phosphatidylserine, phosphatidylcholine and their mixtures) vesicles and divalent cations (Mg2+, Ca2+, Mn2+, etc.) were introduced into the subphase solution of the monolayers. The changes of surface tension of monolayers were measured by the Wilhelmy plate (Teflon) method with respect to divalent ion concentrations and time. When a monolayer of phosphatidylserine and vesicles of phosphatidylserine/phosphatidylcholine (1 : 1) were used, there were critical concentrations of divalent cations to produce a large reduction in surface tension of the monolayer. These concentrations were 16 mM for Mg2+, 7 mM for Sr2+, 6 mM for Ca2+, 3.5 mM for Ba2+ and 1.8 mM for Mn2+. On the other hand, for a phosphatidylcholine monolayer and phosphatidylcholine vesicles, there was no change in surface tension of the monolayer up to 25 mM of any divalent ion used. When a phosphatidylserine monolayer and phosphatidylcholine vesicles were used, the order of divalent ions to effect the large reduction of surface tension was Mn2+ greater than Ca2+ greater than Mg2+ and their critical concentrations were in upon vesicle concentrations as well as the area/molecule of monolayers. For phosphatidylserine monolayers and phosphatidylserine/phosphatidylcholine : 1) vesicles, above the critical concentrations of Mn2+ and Ca2+, the surface tension decreased to a value close to the equilibrium pressure of the monolayers within 0.5 h. This decrease in surface tension of the monolayers is interpreted partly as the consequence of fusion of the vesicles with the monolayer membranes. The order and magnitude of divalent cation concentrations at which phosphatidylserine/phosphatidylcholine (1 : 1) and phosphatidylserine vesicle suspensions showed a large increase in turbidity were similar to those obtained in the above mentioned experiments.

Cations, Divalent↗
PubMed1979

Prostaglandin hydroperoxidase, an integral part of prostaglandin endoperoxide synthetase from bovine vesicular gland microsomes.

The highly purified prostaglandin endoperoxide synthetase from bovine vesicular gland microsomes had two still unresolved enzyme activities; the oxygenative cyclization of 8,11,14-eicosatrienoic acid to produce prostaglandin G1 and the conversion of the 15-hydro-peroxide of prostaglandin G1 to a 15-hydroxyl group, producing prostaglandin H1. The latter enzymatic reaction required heme and was stimulated by a variety of compounds, including tryptophan, epinephrine, and guaiacol, but not by glutathione. A peroxidatic dehydrogenation was demonstrated with epinephrine or guaiacol in the presence of various hydroperoxides, including hydrogen peroxide and prostaglandin G1. Higher activity and affinity were observed with the 15-hydroperoxide of eicosapolyenoic acid, especially those with the prostaglandin structure. Both the dehydrogenation of epinephrine or guaiacol and the 15-hydroperoxide reduction of prostaglandin G1 were demonstrated in nearly stoichiometric quantities. With tryptophan, however, such a stoichiometric transformation was not observed. The peroxidase activity as followed with guaiacol and hydrogen peroxide and the tryptophan-stimulated conversion of prostaglandin G1 to H1 were not dissociable as examined by isoelectric focusing, heat treatment, pH profile, and heme specificity. The results suggest that the peroxidase with a broad substrate specificity is an integral part of prostaglandin endoperoxide synthetase which is responsible for the conversion of prostaglandin G1 to H1.

Animals↗
PubMed1979

Membrane potential of squid axons: effect of internal and external ion concentration.

Transmembrane resting potentials of squid axons were measured with variation of intracellular salt concentrations. It was found that the dependence of resting potential on the extracellular K-ion concentration was practically unaffected by the change of ionic strength in the intracellular phase, and the relationship of membrane potential and the logarithm of extracellular K-ion concentration was a straight line with a slope of about 50 mV/10-fold extracellular K-ion concentration. Also, the degree of change in resting potential due to the change of intracellular K-ion concentration was not affected appreciably by the extracellular solution with various K-ion concentrations, and the membrane potentials were insensitive over a wide range of intracellular K-ion concentrations. It was also indicated that the observed transmembrane potentials are not explained by a conventional membrane potential theory.

Animals↗
PubMed1978

Surface potential of phosphatidylserine monolayers. I. Divalent ion binding effect.

Surface potentials of phosphatidylserine monolayers have been measured in the presence of different divalent ion concentrations in order to determine the way in which divalent ions bind to the membrane surface. The association constants for divalent ions (Mg2+, Ca2+ and Mn2+) with the phosphatidylserine membrane have been obtained from the experimental data and simple ion binding theory. The order of divalent ion binding to the membrane is Mn2+ greater than Ca2+ greater than Mg2+. However, none of the divalent ions used completely neutralized the negative charge of phosphatidylserine even at relatively high concentrations. The amounts of the divalent ions bound depended upon the concentration of the monovalent ions present in the subphase. It is suggested that the amounts of bound ions obtained from the use of radioisotope tracer methods may include a considerable contribution from the excess free ions in the double layer region of the phosphatidylserine membrane.

Binding Sites↗
PubMed1978

Prostaglandin endoperoxide synthetase from bovine vesicular gland microsomes. Inactivation and activation by heme and other metalloporphyrins.

Prostaglandin endoperoxide synthetase purified to apparent homogeneity from bovine vesicular gland microsomes contained iron far below the equimolar amount and essentially no heme. However, the enzyme required various metalloporphyrins including hematin or several hemoproteins such as hemoglobin. Preincubation of the enzyme with hematin or hemoglobin resulted in the loss of enzyme activity. The enzyme inactivation was protected by tryptophan or various other aromatic compounds. Furthermore, the simultaneous presence of tryptophan brought about activation of enzyme; namely, the enzyme preincubated with heme and tryptophan showed an almost full activity with a heme concentration in the reaction mixture far below the saturating level. Such inactivation and activation of the enzyme were also observed with manganese protoporphyrin. An identical heme requirement, heme-induced inactivation, and activation of the enzyme were observed in three types of reactions catalyzed by the enzyme: 1) bis-dioxygenation of 8,11,14-eicosatrienoic acid to produce prostaglandin G1, 2) 15-hydroperoxide cleavage of prostaglandin G1 to produce prostaglandin H1, and 3) guaiacol peroxidation. When heme was replaced by manganese protoporphyrin, the enzyme catalyzed only the bis-dioxygenation producing prostaglandin G1 and the activities of the latter two reactions were not detectable.

Animals↗
PubMed1977

Calcium-induced interaction of phospholipid vesicles and bilayer lipid membranes.

The interaction of unilamellar phospholipid vesicles with bilayer lipid membranes has been studied by observing the electrical conductance of the planar membrane. The presence of phosphatidylcholine vesicles as well as phosphatidylcholine/phosphatidylserine (1 : 1) vesicles on one side compartment of the bilayer membrane, but not phosphatidylserine vesicles, causes discrete fluctuations in the phosphatidylserine membrane conductance, which is also increased by at least an order of magnitude. These events are dependent on vesicle concentration as well as the presence of Ca2+. The results are interpreted in terms of the incorporation of domains of phosphatidylcholine into the membrane, which confer a higher conductance state.

Calcium↗
PubMed1977

Inhibition of prostaglandin endoperoxide synthetase by thiol analogues of prostaglandin.

A variety of thiol compounds inhibited the enzymatic bis-oxygenation of 8,11,14-eicosatrienoic acid to prostaglandin G1, as examined with a purified preparation of prostaglandin endoperoxide synthetase (prostaglandin synthase; 8,11,14-eicosatrienoate, hydrogen-donor:oxygen oxidoreductase; EC 1.14.99.1) from bovine vesicular gland. The hydroperoxide cleavage of prostaglandin G1 producing prostaglandin H1 was not affected by these thiol compounds. Several prostaglandin analogues with a thiol group (9,11-dihydroxy-15S- or 15R-mercaptoprosta-5,13-dienoic acid, 1-mercapto-9,11,15-trihydroxyprosta-5,13-diene, and 1-mercapto-9-oxo-11,15-dihydroxyprosta-5,13-diene) were most potent inhibitors, showing almost complete inhibition at concentrations on the order of 1 muM. Other thiol compounds, such as 2,3-dimercaptopropanol, dithiotherreitol, and dihydrolipoic acid, were also inhibitory but were much less effective. The inhibition, as examined with 9,11-dihydroxy-15S-mercaptoprosta-5,13-dienoic acid and 2,3-dimercaptopropanol, was noncompetitive.

8,11,14-Eicosatrienoic Acid↗
PubMed1976

Fusion in phospholipid spherical membranes. II. Effect of cholesterol, divalent ions and pH.

Effect of cholesterol, divalent ions and pH on spherical bilayer membrane fusion was studied as a function of increasing temperature. Spherical bilayer membranes were composed of natural [phosphatidylcholine (PC) and phosphatidylserine (PS)] as well as synthetic (dipalmitoyl-PC, dimyristoyl-PC and dioleoyl-PC) phospholipids. Incorporation of cholesterol into the membrane (33% by weight) suppressed the fusion temperature and also greatly reduced the percentage of membrane fusion. The presence of 1 mM divalent ions (Ca++, Mg++ or Mn++) on both sides or one side of the PC membrane did not affect appreciably its fusion characteristic with temperature, but the PS membrane fusion with temperature was greatly enhanced by the presence of divalent ions. The variation of pH of the environmental solution in the range of 5.5 approximately 7.0 did not affect the membrane fusion characteristic. However, at pH 8.5, the fusion with respect to temperature was shifted toward the lower temperature by approximately 3degreesC for PC and PS membranes, and at pH 3.0 the opposite situation was observed as the fusion temperature was increased by 6degreesC for PS membranes and by 4degreesC for PC membranes The results seem to indicate that membrane fluidity and structural instability in the bilayer are important for membrane fusion to occur.

Calcium↗
PubMed1976

The levels of main urinary metabolite of prostaglandin F1alpha and F2alpha in human subjects measured by radioimmunoassay.

Radioimmunoassay technique for measuring 5alpha, 7alpha-dihydroxy-11-keto-tetranorprosta-1, 16-dioic acid, the main urinary metabolite of PGF1alpha and PGF2alpha (PGF2alpha-MUM), was further improved. It was postulated based on some experimental data that the PGF2alpha-MUM exists in the urine mostly as dioic acid form, not as delta-lactone form the daily excretion of PGF2alpha-MUM in men ranged from 14.43 mug to 36.14 mug and in women from 5.21 mug to 14.25 mug.

Female↗