Binding of folates to Dictyostelium discoideum cells. Demonstration of five classes of binding sites and their interconversion

Wit, R. J. W. D. & Haastert, P. J. M. V., 1985, In : Biochimica et Biophysica Acta - Biomembranes. 814, 2, 15 p.

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Studies of the binding of four folate derivatives to the cell surface of Dictyostelium discoideum indicate the existence of five types of sites. About 99% of the total number of binding sites (160000 per cell) belongs to the 'non-selective' type, which recognizes folate, 2-deaminofolate and methotrexate with equal affinity. As judged by the kinetics of association and dissociation this class consists of two distinct subtypes; a high-affinity site, designated by AH, and a low-affinity site AL. Upon addition of ligand a number of the low-affinity sites is converted to the high-affinity state. Prolonged dissociation revealed the presence of extremely slowly dissociating sites. While the A-sites released bound ligand within 5 s, the slow (B) type yielded a half-time of about 6 min. This class (550 sites per cell) showed a clear selectivity for the four folates, with N10-methylfolate being the best ligand. From the kinetics of association and dissociation it is concluded that the B-sites are interconvertible with another binding type. In addition a class of sites was detected, which binds N10-methylfolate and folate with high affinity but 2-deaminofolate and methotrexate with approx. 100-fold lower affinity. Kinetic studies reveal that this C-class is also composed of two subtypes; a fast equilibrating site (within 1 s) designated as CF, and a slower site CS. It is proposed that before binding of ligand only CF exists, while after binding this binding type is converted into CS. At equilibrium more than 90% of the C-sites have attained the CS state.
Original languageEnglish
Number of pages15
JournalBiochimica et Biophysica Acta - Biomembranes
Issue number2
Publication statusPublished - 1985


  • (D. discoideum), Receptor interconversion, Cell-surface receptor, Folate binding

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