The binding of vanadium (V) oligoanions to sarcoplasmic reticulum

The binding of monovanadate and decavanadate anions to sarcoplasmic reticulum vesicles was measured by equilibrium sedimentation. The affinity of vanadate binding and the molar amount of vanadium (V) bound at equilibrium is much greater with decavanadate than with monovanadate. The binding data can be rationalized in terms of one binding site per ATPase molecule for monovanadate and two sites per ATPase for decavanadate. The Ca-ATPase crystals formed with monovanadate and with decavanadate are similar in appearance, but decavanadate is particularly effective in promoting the crystallization of Ca2+-ATPase at low V concentration (10-100 microM) in a Ca2+-free medium.