Richard F. Sprecher

Magnetic resonance study of 5′-ATP binding to hemocyanin

Abstract The oxidation state of copper in oxyhemocyanin is uncertain, since it does not display a copper(II) electron paramagnetic resonance signal unless the protein is denatured. We have utilized proton and phosphorus magnetic resonance line broadening techniques in studying the binding of 5′-ATP to hemocyanin. Our data indicate that the copper at the oxygen-binding site is at least partly copper(II). The apparent binding constant for 5′-ATP to Busycon hemocyanin is 28 M−1 and to Limulus hemocyanin is 15 M−1. These values have been determined from proton magnetic resonance data, in the pD range 7.4–8.2, at 32°C. EPR spectroscopy is not a sensitive method to detect the binding of ATP to oxyhemocyanin.