Inorganic phosphate uptake by protoplasts and whole cells of yeast Candida tropicalis: absence of high affinity transport system in protoplasts.

Pi-uptake by protoplasts obtained from the yeast Candida tropicalis as well as in whole cells is an energy dependent process. However, the apparent affinity constant of Pi transport by protoplasts about 0.4-0.5 mM whereas Km of 5-6 microM, occurs in whole cells as previously shown. Therefore it can be concluded that protoplasts take up actively Pi but the high affinity capacities are lost. In addition, the Pi-binding proteins are released during protoplasts formation. The presence of Pi-binding proteins in the "cellulase fluid" is demonstrated by immunological tests and by their binding activities after partial purification. These results are in good agreement with the involvement of Pi-binding proteins in Pi uptake in the yeast Candida tropicalis.