In this study we used a newly isolated Yarrowia lipolytica strain with a un
ique capacity to grow over a wide pH range (3.5-10.5), which makes it an ex
cellent model system for studying phosphate transport systems in cells grow
n under alkaline conditions. Phosphate uptake by Y. lipolytica yeast cells
grown at pH 9.5-10 was shown to be mediated by several kinetically discrete
Na+-dependent systems, One of these, a low-affinity transporter, operates
at high P-i concentrations and is, to our knowledge, here kinetically chara
cterized for the first time, The other two high-affinity systems are derepr
essible, come into play under conditions of P-i-starvation, and appear to b
e controlled by the availability of extracellular P-i, They represent the f
irst examples of high-capacity, Na+-driven P-i transport systems in an orga
nism belonging to neither the animal nor the bacterial kingdoms.