INFLUENCE OF GLUCOSE AND OTHER SUBSTRATES ON ELECTRIC-FIELD AND POLYETHYLENE GLYCOL-MEDIATED TRANSFORMATION OF INTACT YEAST-CELLS

A prepulse incubation with 2% glucose (mannose, fructose) strongly inhibited electrotransformation of intact yeast cells. This inhibitory effect was not due to alterations of cell viability or to cell membrane electropermeabilization, and was not affected by the solution buffer properties of preincubation and pulsing media. The electrotransformation efficiency was not modified by non-metabolized substances, such as sorbitol or alose. The glucose inhibition of electrotransformation was fast, occurring after only a 3-5-min preincubation. The postpulse incubation with substrate also decreased transformation efficiency, but was pH-dependent. We observed a similar, strong inhibitory effect of glucose when cells were transformed chemically. A pH dependence of yeast electrotransformation was established.