A Specific Effect of Copper on the Respiration of Chlorella vulgaris

Abstract

ON adding heavy metal salts to cells of Chlorella vulgaris shaken in 10⁻³ M phosphate buffer, pH 6.0, the endogenous respiration often increased temporarily but, with the exception of silver, high concentrations caused no respiratory inhibition for many hours. Copper, however, differed from all other metals tested (barium, manganese, nickel and lead inter alia) in that its effect on respiration depended on the environmental conditions during the period of treatment. If the suspensions of Chlorella were shaken continuously, 10⁻¹ M copper sulphate was not inhibitory for 7–20 hr., but if the shaking was stopped, concentrations lower than 10⁻³ M rapidly became toxic. Experiments were carried out in respirometer flasks, using about 3 × 10⁸ cells suspended in 3 ml. of buffer. Copper was determined by the method of Abbott and Polhill¹. Copper sulphate was tipped from the side-arms, and shortly afterwards one set was brought to rest while the remainder was shaken for 3 hr. Thereafter, caustic soda was added to the centre wells of the flasks, which were then shaken for a further period during which respiration was measured. The toxic effect on unshaken cells increased if the treatment was carried out in narrow centrifuge tubes.