Cudraniaxanthone and butyrospermol acetate from the roots of Cudrania javanensis

A new xanthone, cudraniaxanthone has been isolated from Cudrania javanensis and its constitution established. Butyrospermol, its acetate (first isolation from a natural source), kaempferol, aromadendrin, populnin, quercetin and taxifolin have also been obtained.     

Noncontact dipole effects on channel permeation. III. Anomalous proton conductance effects in gramicidin

Proton transport on water wires, of interest for many problems in membrane biology, is analyzed in side-chain analogs of gramicidin A channels. In symmetrical 0.1 N HCl solutions, fluorination of channel Trp(11), Trp-(13), or Trp(15) side chains is found to inhibit proton transport, and replacement of one or more Trps with Phe enhances proton transport, the opposite of the effects on K(+) transport in lecithin bilayers. The current-voltage relations are superlinear, indicating that some membrane field-dependent process is rate limiting. The interfacial dipole effects are usually assumed to affect the rate of cation translocation across the channel. For proton conductance, however, water reorientation after proton translocation is anticipated to be rate limiting. We propose that the findings reported here are most readily interpreted as the result of dipole-dipole interactions between channel waters and polar side chains or lipid headgroups. In particular, if reorientation of the water column begins with the water nearest the channel exit, this hypothesis explains the negative impact of fluorination and the positive impact of headgroup dipole on proton conductance.     

Study of the interaction of Saccharomyces cerevisiae with glucose by particle microelectrophoresis

Saccharomyces cerevisiae NCYC 239 in the presence of glucose at temperatures under 303 K shows a time-dependent lowering of electrophoreric mobility $\text{υ}$. At temperatures above 303 K, this time-dependent change in $\text{υ}$ is in the direction of increased mobilities. Cells suspended in buffer indicate a surface pK_a of less than 4, whereas for cells suspended in buffered glucose it is impossible to derive a surface pK_a. A kinetic study of the interaction of S. cerevisiae with glucose as a function of temperature allows calculation of an activation energy of 140 kJ·mol^?1 for the combined processes of (i) uptake of glucose onto the cell wall, (ii) transfer through the cell wall and membrane, and (iii) the establishment of a steady glucose flux through the wall and membrane.