Reversible binding of the chemoattractant folic acid to cells of Dictyostelium discoideum.

The chemoattractant folic acid binds reversibly to receptors at the surface of Dictyostelium cells. In undifferentiated cells (t0.5) 6 X 10(4) binding sites per cell with a K0.5 value of 1.5 X 10(-7) M were determined. The number of folic acid receptors per cell decreases slightly during cell development. In differentiated cells (t10) 3.3 X 10(4) binding sites per cell were estimated. The folic acid binding sites appear to be specific for folic acid and its derivatives. 2-Deamino-2-hydroxyfolic acid, 4-amino-folic acid (aminopterin), and 4-amino-10-methylfolic acid (amethopterin) compete for the folic-acid-binding sites. Nor do adenosine 3',5'-phosphate and guanosine 3',5'-phosphate affect binding of folic acid. The folic acid receptors appear to be distinct from the catalytic sites of the membrane-bound folic acid deaminase.