Salt stimulated respiration of Chlorella fusca.

ATP contents have been measured before and after addition of KCl (5 mM final concentration) to suspensions of Chlorella in distilled water under different conditions of energy supply. The levels decreased immediately after salt addition and returned to the original values under conditions both of oxidative phosphorylation and of cyclic photophosphorylation, but not under conditions of fermentation. It appears that this decrease in the ATP level is the cause for salt stimulated respiration (S.S.R.). Furthermore, it is shown that cycloheximide and EDTA, which interact with Rb+ uptake (active and ATP-driven) at low salt concentration, also reduce S.S.R. From this parallelism it is concluded that the ATPase involved in Rb+ uptake at low salt concentration is also responsible for S.S.R. at high salt concentration. As S.S.R. provides far more energy than is required for the small influx of ions it is suggested that the ATPase is decoupled by the salt from ion transport.