Toshiyuki Akiyama

The molecular dynamics of cholesterol in bilayer membranes: A deuterium NMR study☆

Abstract The 2 H-NMR spectra of selectively deuterated cholesterol, intercalated in egg phosphatidyl-choline, were examined. The orientation of the axis of motional averaging was calculated using the observed quadrupole splittings and the atomic coordinates. With the known orientation of the rotation axis, quadrupole splittings observed for deuterium labels on cholesterol can be related to the molecular order parameter of the sterol. In addition, knowledge of the axis orientation allows prediction of the magnitudes of quadrupole splittings for deuterium at other positions, which is useful in the choice of labelling for particular applications. Finally, preliminary relaxation time measurements yield information on the rates of anisotropic motion of cholesterol in bilayer membranes.

A new sapogenin in the saponins of Zizyphus jujuba, Hovenia dulcis and Bacopa monniera

Abstract Acid hydrolysis of the saponin of the seeds of Zizyphus jujuba afforded ebelin lactone, which yielded the sapogenin, jujubogenin, on Smith-de Mayo degradation. The mechanism of conversion of jujubogenin into ebelin lactone has been elucidated. Hovenoside G of Hovenia dulcis and bacoside A of Bacopa monniera which produce ebelin lactone on acid hydrolysis have also been found to yield jujubogenin on Smith-de Mayo degradation.

Phosphatidylcholine liposomes containing cholesterol analogues with side chains of various lengths

The effect of the length of the side chain of sterols on their interaction with phosphatidylcholine was studied by measuring the permeability properties of liposomes constituted with sterol analogues with side chains of various lengths. The sensitivities of liposomes constituted with these sterol analogues toward digitonin and polyene antibiotics were also examined. The effects of sterols on phase transition of phosphatidylcholine were examined by measuring their effects on permeability increase due to perturbation of phase equilibrium and by differential scanning calorimetry. An analogue with a short side chain, isopropyl (C-22), had a very similar effect to cholesterol in suppressing the permeability increase, suggesting that the full length of the side chain is not necessary for this effect. The permeability of egg yolk phosphatidylcholine at 42 degrees C was suppressed as much by the analogue C-22 as by cholesterol. Androstene-3-beta-ol, an analogue without a side chain, however, had little suppressive effect. Thus it is concluded that the condensing effect of sterol requires a side chain, but not the full length of side chain. Liposomes constituted with analogues having a side chain with more than 5 carbon atoms showed maximum reactivity with a polyene antibiotic, amphotericin B, whereas those constituted with analogues having a side chain with less than 4 carbon atoms showed weaker reactivity. These findings indicate that a side chain with more than 5 carbon atoms is essential for the maximum interaction of liposomes with amphotericin B. Unlike amphotericin B, filipin reacted almost equally well with liposomes containing C-22 and with those containing cholesterol. Thus the chain length of the side chain of sterol is less important for interaction of liposomes with filipin than for their interaction with amphotericin B. Liposomes containing analogues having a side chain with more than 6 carbon atoms showed maximum reactivity with digitonin. Thus for the maximum interaction of liposomes with digitonin, the side chain of sterol should be longer than 6 carbon atoms.

The structure of jujubosides A and B, the saponins isolated from the seeds of Zizyphus jujuba

Abstract Stepwise chemical and enzymatic hydrolyses of jujubosides A and B, the saponins of the seeds of Zizyphus jujuba , afforded prosapogenins I, II and III. The sequence and configuration of the sugar linkages in the saponins and the pro-sapogenins were determined from the PMR data and the application of Klynes rule of molecular rotations and structures were assigned to jujubosides A and B.