A method of estimating phosphagen and some other phosphorus compounds in muscle tissue

THE exact nature of phosphagen is not yet known. A protein-free extract of striated muscle contains a compound of creatine and phosphoric acid which may be identical with but is more probably derived from the phosphagen originally present in the muscle. It seems advisable to retain the term phosphagen for the substance existing in the muscle, reserving the chemical description creatinephosphoric acid for the substance isolated from acid extracts of muscle. Mr H. V. Horton, working in this laboratory, has shown that although phosphagen cannot diffuse from a living muscle, creatinephosphoric acid can diffuse readily through collodion membranes. This is true whether the creatinephosphoric acid has been extracted from the muscle by means of acid, dilute alkali, or alcohol. The inability of phosphagen to diffuse from living muscles may be due to the selective impermeability of the muscle cells to the creatinephosphoric anion, but it seems more justifiable to suppose that creatinephosphoric acid exists in the muscle in combination with some colloidal substance. Certainly the view that creatinephosphoric acid exists as such in the muscle, and that its disappearance in fatigue is a result of simple hydrolysis, raises serious difficulties. Meyerhof and Lohmann (1) have shown that creatinephosphoric acid has a large heat of hydrolysis, about 11,000 calories per gram molecule, but the total heat of contraction of a muscle has the same value relative to the lactic-acid production whether much or little phosphagen disappears simultaneously. Consideration of the myothermal data available leads us to the conclusion that the "breakdown " and "resynthesis " of phosphagen in a living muscle are reactions involving very little energy. (See A. V. Hill (2).) The only available means of determining the amount of phosphagen in muscle is to estimate the creatinephosphoric acid in a protein-free