Functional mitochondria with respiratory control were isolated from the yeasts Saccharomyces cerevisiae and Schwanniomyces castellii. The presence of site I in Schw. castellii was indicated by higher ADP/O ratio than in S. cerevisiae where this site is absent. The ATPase V-max was higher in S. cerevisiae than in Schw. castellii mitochondria. The latter was increased by the DR12 nuclear mutation. Nevertheless, the stimulation by heat and the inhibition profile of oligomycins on mitochondrial F1-F0 ATPase activities were similar in all three tested strains. In S. cerevisiae and Schw. castelli wild type or mutant mitochondria, the well-known inhibition of F1-F0 ATPase activity by low concentrations of oligomycins is abolished at high inhibitor concentrations near 60 mug/ml suggesting uncoupling of F1 activity. At still higher oligomycin concentration the ATPase activity of both species and mutant is again strongly inhibited, suggesting an inhibitory effect on yeast F1 activity not detected so far. (C) 2004 Elsevier Inc. All rights reserved.