title: Modulation of interleukin 2 high-affinity binding by lymphocyte-derived tetrahydrobiopterin: pterins as potential participants in the control of interleukin 2 receptor assembly.
abstract: In this report, we have examined whether (6R)-tetrahydrobiopterin (H4biopterin) modulates the binding of interleukin 2 to high-affinity sites of the cloned mouse cytotoxic T-lymphocyte clone CTLL-2. Scatchard plot analysis of the equilibrium binding data reveals increased affinity when the cells are exposed simultaneously to interleukin 2 and to the pterin. The Kd values are statistically significantly reduced from 1.4 x 10(-11) M to 0.78 x 10(-11) M interleukin 2. The dissociation kinetics of the ligand were followed at 4 degrees C after equilibrium binding under high-affinity conditions (1.2 x 10(-10) M interleukin 2). In the presence of H4 biopterin, the dissociation rate constant (k-1) decreases from 6.2 x 10(-3) min-1 to 3.0 x 10(-3) min-1 and the half-time for dissociation increases from 106.8 min to 218.0 min. As a third approach interleukin 2 was bound to the surface of cells under high-affinity conditions by incubation in the cold and the internalization kinetics upon warming were determined. Sigmoidal-shaped kinetics of endocytosis in control cells indicate that the internalization rates increase only gradually. The presence of H4 biopterin causes an apparent immediate transition from higher-order kinetics to a linear response so that maximum internalization rates are reached immediately upon warming. The data show that lymphocyte-derived H4 biopterin in vitro at concentrations ranging from 2-8 x 10(-7) M modulates interleukin 2 high-affinity binding and that H4 biopterin potentially participates in the control of interleukin 2 receptor assembly.
authors.affiliation: Gesellschaft für Strahlen- und Umweltforschung München, Institut für Experimentelle Hämatologie, München, Federal Republic of Germany.
authors.forename: I
authors.initials: I
authors.lastname: Ziegler
authors.forename: U
authors.initials: U
authors.lastname: Schwuléra
mesh_terms: D001665:Binding Sites / Q000187:drug effects; D001708:Biopterins / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000502:physiology; D002999:Clone Cells / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D007376:Interleukin-2 / Q000378:metabolism*; D007700:Kinetics; D015375:Receptors, Interleukin-2 / Q000378:metabolism*; D013602:T-Lymphocytes, Cytotoxic / Q000187:drug effects* / Q000378:metabolism
chemical_list: D007376:Interleukin-2; D015375:Receptors, Interleukin-2; D001708:Biopterins; C003402:sapropterin