Some properties of the adenosine triphosphatase systems of two yeast species, saccharomyces cerevisiae and rhodotorula glutinis

Abstract

Total ATPase levels were determined in homogenate fractions of baker's yeast,Saccharomyces cerevisiae K andRhodotorula glutinis. The maximum ATPase activities in 8000 × g supernatant of the three yeast strains were 6.0, 1.9, and 2.2 mmol P_i h⁻¹ (g DS)⁻¹, respectively; the activities in the sediment were somewhat higher. Exponential cells ofS. cerevisiae K andR. glutinis exhibited higher ATPase levels than did the stationary cells. The total ATPase activity in both yeast species showed a maximum at pH 6.8, a minimum at pH 7.2, and another broader maximum around pH 8.0. No significant Na,K-ATPase activity was detected in baker's yeast, in either the exponential or the stationary cells ofR. glutinis, and in exponentialS. cerevisiae K cells in the pH range of 6.0–9.0. Stationary cells ofS. cerevisiae K exhibited, at pH 7.0–8.5, a Na,K-ATPase activity attaining 9% of total ATPase level. 3 × 10⁻³ m phenylmethyl sulphonyl fluoride had no effect on the total ATPase level inS. cerevisiae and inhibited the activity inR. glutinis by 25%; it did not bring forth any Na,K-ATPase activity apart from that found in its absence. 1.5m urea lowered the ATPase activity inR. glutinis by 68% but had no effect onS. cerevisiae cells. 10⁻⁵ m dicyclohexylcarbodiimide suppressed the ATPase activity inS. cerevisiae andR. glutinis by 74 and 79%, respectively. Neither agent revealed any additional Na,K-ATPase activity. The comparison of Na,K-ATPase activities with data on K⁺ fluxes across the yeast plasma membrane suggested that even with the lowest flux values the Na,K-ATPase, even if present, would account for a mere 40% of transported ions. The results imply that the active ion transport in yeasts is energized by mechanisms other than the Na,K-ATPase.