Transport of nutrients in yeast protoplasts

Protoplasts were prepared with snail-gut juice from Saccharomyces cerevisiae and Candida utilis. Transport of D-xylose (A), trehalose (B), 2-deoxy-D-glucose (C), L-leucine (D), L-proline (E), inorganic phosphate (F) and H+ ions (G) was studied with special emphasis on the first species. Transport of A which is not sensitive to glucose stimulation in its synthesis was not affected by protoplast formation. Similarly unaffected were transports of B, D, E and F in their "residual" form in starved cells. However, transport of these substances after glucose-stimulated synthesis was practically fully suppressed by protoplast formation. This may be connected with the virtually complete inhibition of the proton pump (G) in protoplasts with the implication that B, D, E and F are transported in conjunction with protons but only those that are immediately produced by the proton pump (glucose consumption, oxygen utilization and membrane potential were not substantially altered in protoplasts). Transport of C was stimulated nearly two-fold in protoplasts. Uranyl ions (0.1 mM) had a pronouncedly lower inhibitory effect on all the transports studied in protoplasts.