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Abstract
The electron spin resonance spectrum of a water-soluble nitroxide free radical TEMPOL has been measured in concentrated suspensions of sarcoplasmic reticulum vesicles. Spectra observed in the presence of a high steady-state concentration of phosphoenzyme, formed from inorganic phosphate in the presence of Mg 2+, have been compared with those observed in the absence of phosphoenzyme. Quite large and reproducible differences in the two spectra were observed. Below 0 ° C the bulk water froze, and TEMPOL accumulated into a residual liquid phase of high microscopic viscosity, and of polarity slightly less than water. When lipids were extracted from the vesicles, dispersed in water and frozen, the residual signal from TEMPOL showed that it was in an environment of polarity similar to ethanol. It is proposed that the water which did not freeze at 0 ° C was contained in the hydrophobic cleft of the ATPase containing the active site. Like water in small hydrophobic pores of synthetic polymers, it consisted of large strongly-bonded clusters, and had high viscosity, low entropy and profoundly changed solvent properties.
Published Version
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