Water coordination by heme iron in metmyoglobin.

Using electron spin echo envelope spectroscopy, we have proven that the water close to heme in metmyoglobin is bound to the iron. For protein samples exchanged against D2O, we show that the electron nuclear coupling for 2H is 0.8 MHz. This coupling is considerably smaller in methemoglobin, pointing out a fundamental difference in bonding to water.