Further observations on phosphagen

THE collection of experimental results presented in this paper is too inconsecutive to be used as the basis of any theoretical discussion of phosphagen, but the results are published in the hope that they will be of practical use to other workers in the field of muscle chemistry. Phosphagen is the name given to a substance which is present in considerable quantities in resting voluntary muscle, and is of the nature of an ester of phosphoric acid, remarkable for the ease with which the phosphoric acid is hydrolysed off in dilute acid solution. From the skeletal muscles of rabbits we have isolated a material which shows this typical lability and which is a compound of creatinel and phosphoric acid(l). But it is not yet certain whether this substance is identical with, or is a breakdown product of, phosphagen. The extreme lability of phosphagen in acid solution makes it imperative that its extraction by the following method from the muscle should be completed in the minimum of time. To precipitate proteins in the least bulkT and most easily filtrable form, 4 p.c. CC13COOH has been found best (40 c.c. per grm. of muscle), filtration being carried out within 12 minutes of the grinding of the muscle. It is not at present possible to discover by direct estimation whether the phosphagen extraction is complete in this time: presumably it is, since the sum of the phosphagen and inorganic phosphate extracted is not increased by longer extraction (up to 24 hours). Neither is there any appreciable increase in the amounts extracted of creatine, lactic acid, or acid-soluble organic phosphorus (Table I). Even with an extraction as short as 10 minutes there nevertheless occurs some breakdown of the extracted phosphagen in the acid medium. If phosphagen be dissolved in 4 p.c. CC13COOH at a dilution comparable to a muscle extract, at room temperature half of it is hydrolysed in