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Guanine nucleotides modulate the ligand binding properties of cell surface folate receptors in Dictyostelium discoideum
Author(s) -
De Wit René J.W.,
Bulgakov Roman
Publication year - 1985
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(85)80530-5
Subject(s) - dictyostelium discoideum , gtp' , guanine , nucleotide , cooperative binding , cooperativity , biochemistry , binding site , receptor , chemistry , ligand (biochemistry) , enzyme , gene
Dictyostelium discoideum cells show 2 distinct classes of cell surface binding sites for folates. One type is non‐specific, i.e., binds folic acid (FA), 2‐deaminofolic acid (DAFA), and methotrexate (MTX) with similar affinity ( K 0.5 ⋍ 140 nM). Scatchard analysis of this non‐specific binding type suggests either heterogeneity or negative cooperativity. Isolated D. discoideum membranes show similar binding characteristics. Guanine nucleotides changed the binding levels of [ 3 H]MTX. In the presence of 0.1 mM GTP, the number of binding sites remains unchanged, while the affinity decreases. GDP and guanylyl imidodiphosphate (GPPNP) are required at about 20‐fold higher concentration than GTP, which elicits a half‐maximal effect at 15μM. Other guanine and adenine nucleotides are ineffective up to 1 mM. These results suggests that the non‐specific cell surface receptor for folic acid interacts with a guanine nucleotide regulatory (G‐) protein.