Use of modified adenine nucleotides in mechanistic studies on oxidative phosphorylation: structure and space at the catalytic site.

This report summarizes structure/activity investigations on 3'-O-substituted adenine nucleotides derived from 3'-O-naphthoyl-ADP. Among these are fluorescent nucleotides, which allow one to differentiate between two types of binding sites on the inner surface of the mitchondrial inner membrane. One type of site is highly fluorescent but is not located on F1. It is attributed to the nucleotide carrier, because it stays on the membrane when F1 is removed. The other type of sites, giving no or only very low fluorescence, is located on F1 and shows high affinity to these analogs, which is modulated by the energy state of the membrane. On the basis of kinetic data, stability of magnesium complexes, and fluorescence properties, conclusions are drawn on the probable conformation of these nucleotides in the bound state. They allow one to explain why these nucleotide analogs are extremely strong inhibitors of oxidative phosphorylation and photophosphorylation, why the ADP derivatives cannot be phosphorylated, and why the ATP analogs are no substrates of ATPase. Furthermore, the results allow some insight into the mechanism of phosphorylation and the structural properties at the catalytic site.