Formation of the stable myosin-ADP-aluminum fluoride and myosin-ADP-beryllium fluoride complexes and their analysis using 19F NMR.

The effects of aluminum fluoride and beryllium fluoride on smooth muscle myosin and its subfragments were studied. Mg(2+)-ATPase activity was inhibited in the presence of aluminum fluoride (beryllium fluoride). [3H]ADP bound to heavy meromyosin (HMM) in the presence of aluminum fluoride (beryllium fluoride) and was not dissociated after 3 days of dialysis demonstrating that [3H]ADP was trapped in HMM. These results suggest the formation of a stable HMM-ADP-fluoroaluminate (fluoroberyllate) complex. The intrinsic tryptophane fluorescence intensity was increased in the presence of ADP and aluminum fluoride (beryllium fluoride). Acto-S1 was dissociated upon the formation of S1-ADP-fluoroberyllate and actin destabilized S1-ADP-fluoroberyllate complex, while S1-ADP-fluoroaluminate failed to bind to actin. Furthermore, when S1 formed the complex with actin, nucleotide trapping did not occur in the presence of fluoraluminate. These results indicated that the myosin-ADP-fluoroberyllate complex resembles a weak binding state while myosin-ADP-fluoroaluminate complex is a distinct conformation although the binding to actin was also weak. The structure of the ternary complex was investigated using 19F NMR. The 19F NMR spectrum of the S1-ADP-fluoroaluminate complex showed a peak at -66.7 ppm which is due to the binding of fluoraluminate to S1. The peak was not observed when 5'-adenylylimidodiphosphate was substituted for ADP suggesting that aluminum fluoride plays a role as a phosphate analogue. The stoichiometry of the bound fluoride was determined to be 3.8 mol/mol S1 suggesting that the bound species is AlF-4.