Nitrogenous Muscle Extractives *

Studies of the chemical alterations in muscle, associated with its activity, have been well summarized by Eggleton1", Meyerhof97, and Milroy"'0. Such summaries naturally include a discussion of only those substances which have been shown to take part in the metabolic changes. As the first demonstration of chemical change with muscle activity concerned the change of glycogen to lactic acid, it was natural that research should continue along that line. Embden, Griesbach and Schmitz23 observed an increase in the inorganic phosphate of muscle along with an increase in lactic acid. In studying the organic phosphoric acid compounds of muscle, Embden and Laquer24encountered adenine nucleotide and thus associated the non-protein nitrogenous constituents of muscle with the metabolism concerned with muscle contraction. Fiske and Subbarow"6 showed that much of the creatine of muscle is combined with phosphoric acid but the compound is very unstable. Other nitrogenous compounds of muscle have not yet been shown to be concerned with its intermediary metabolism, but their nearly unique occurrence in muscle, and the relatively high concentration of some, make it appear that they are also associated with the activities of this tissue. It is the purpose of this review to call attention to the best known of the nitrogenous constituents of muscle which have been isolated in pure crystalline form. All the basic compounds which have been isolated from muscle extract, creatine, purines, carnosine, anserine, carnitine and methylguanidine, have been obtained after the use of rather drastic chemical procedures. Protein is removed by boiling the weakly acid extract, which is then often evaporated in the air at 1000 C. Phosphotungstic acid, silver, mercury and lead salts, hydrogen sulfide and barium hydroxide are the reagents most commonly used in the isolations. The solutions are frequently heated and allowed to stand. On the other hand, the acidic compounds, creatine phosphoric acid and adenyl-pyrophosphoric acid, have been obtained with procedures especially designed to guard against decomposition of unstable compounds. Care has even been taken to use freshly excised resting