CHARACTERISTICS OF SULFITE TRANSPORT BY CHLORELLA-VULGARIS

The rate of short-term accumulation of [S-35]sulfite in Chlorella vulg ar is cells was found to be strongly dependent on the pH of the medium . The rate increased with decreased pH, and the increase in rate close ly paralleled the increase in the concentration of the un-ionized form of sulfite. When the pH of the medium was increased, fast accumulatio n ceased immediately. The rate of accumulation showed a strong tempera ture dependence, with an apparent temperature coefficient of 1.93 per 10 degrees C rise, between 10 and 25 degrees C. Because pK(a) values o f sulfite shift with temperature, the rates were corrected by dividing by the concentration of the un-ionized form of sulfite present at the respective temperatures. The temperature coefficient was then found t o decrease to 1.45. When cells which had been allowed to accumulate [S -35]sulfite for 20 min were transferred to a medium containing no sulf ite, more than 50% of the accumulated [S-35] was released into the med ium in 20 min. Our results are compatible with a simple diffusion mode l of SO2 transport into Chlorella cells.