Proton extrusion inSaccharomyces cerevisiae mutants in very dilute suspensions

Substrate-induced H⁺ extrusion was studied in dilute (0.04–0.5 mg dry mass per mL) unbuffered suspensions ofS. cerevisiae. Wild-type strains 196-2 and K and 196-2-derived mutants altered in hexose transport, glucosephosphate isomerase, mannosephosphate isomerase, pyruvate kinase, and arho petite mutant were characterized as to growth, biochemical and H⁺-pumping properties. Their H⁺ extrusion differed, depending on strain, growth conditions, and the H⁺-efflux-inducing substrate; the efficiency of the process depended critically on the balance between substrate uptake, its dissimilation, attendant mobilization of energy sources and build-up of acidity sources in the cell, and the energy supply to H⁺excreting systems.