SPECIATION IN SYSTEMS CONTAINING ALUMINUM, NUCLEOSIDE DIPHOSPHATES, AND FLUORIDE

Al3+ and excess F- are commonly added to G-protein systems containing guanosine diphosphate (GDP), and it has been proposed that AlF4- serves as a tetrahedral pseudophosphate bound to GDP or other nucleoside diphosphate (NDP). In this paper we use F-19 and H-1 NMR to analyze the ternary system Al3+-NDP-F- in aqueous solutions. Ternary complexes (NDP)AlF(x) (x = 1 to 3) are identified, but no (NDP)AlF4 is found. The ternary complex (NDP)AlF appears with a frequency that is equal to that expected statistically on the basis of binary complex stabilities. Under the conditions of maximum effect in G-protein experiments in neutral solutions, most Al3+ occurs as (HO)AlF3-; the lesser amount of nucleoside diphosphate is not competitive. By separately gluing the NDP and AlF4- in close proximity, the protein provides a special environment that links them together.