PERMEATION OF REDOX SPECIES THROUGH A CELL-MEMBRANE OF A SINGLE, LIVING ALGAL PROTOPLAST STUDIED BY MICROAMPEROMETRY

Permeation of several redox species through a cell membrane of a singl e algal protoplast (radius 100 mu m) was investigated by amperometry w ith a Pt microdisk electrode (disk radius, 6.5 mu m) located near the membrane. The redox current observed at the microelectrode decreased a s the microelectrode approached the cell membrane since the membrane a cted as a barrier for diffusion of redox species from bulk to the micr oelectrode. Permeability coefficient (P-m) of the protoplast membrane was determined by the quantitative analysis of the variation of the re dox current with microelectrode-membrane distance using digital simula tion. The P-m values for Fe(CN)(6)(4-), Fe(CN)(6)(3-), Co(phen)(3)(2+) , ferrocenyl methanol(FMA) and p-hydroquinone(QH(2)) were less than or equal to 1.0 X 10(-4), less than or equal to 1.0 X 10(-4), 1.0 X 10(- 3), 5.0 X 10(-3) and 2.0 X 10(-2) cm/s. respectively. Using these P-m values, the concentration changes inside a model cell and chloroplast were theoretically calculated. (C) 1998 Elsevier Science B.V.