The state of water in muscle tissue as determined by proton nuclear magnetic resonance.

The nuclear magnetic resonance (NMR) of water protons in live and glycerinated muscle, suspensions of glycerinated myofibrils, and solutions of several muscle proteins has been studied. T(1) and T(2), measured on partially hydrated proteins by pulsed spin-echo techniques, decreased as the ratio of water to protein decreased, showing that the water which is tightly bound by the protein has short relaxation times. In live muscle fibers the pulse techniques showed that, after either a 180 or a 90 degrees pulse, the relaxation of the magnetization is described by a single exponential. This is direct evidence that a fast exchange of protons occurs among the phases of the intracellular water. The data can be fitted with a model in which the bulk of the muscle water is in a phase which has properties similar to those of a dilute salt solution, while less than 4-5% of the total water is bound to the protein surface and has short relaxation times. Measurements of T(1) and T(2) in protein solutions showed that no change in the proton relaxation times occurred when heavy meromyosin was bound to actin, when myofibrils were contracted with adenosine triphosphate (ATP), or when globular actin was polymerized.