Phosphagen in Mytilus californianus

1. 1. N-phosphorylarginine of muscle extracts of Mytilus californianus, and some other species investigated, gives three distinct spots on two-dimensional chromatography. 2. 2. The three fractions, AP1, AP2 and AP3, had a 1:1 ratio of arginine to phosphate (P). One minute hydrolysis in 0·5 N HCl at 100°C resulted in splitting to arginine and inorganic P. None of the fractions contained either carbohydrate, amino acids other than arginine, or acetyl. AP2 was found to contain Ca 2+. 3. 3. All three fractions were substates for arginine phosphoryltransferase; however, when Mg 2+ was omitted from the assay system only AP1 showed a liberation of free arginine. 4. 4. AP1, AP2 and AP3 differed in the rate of incorporation of either arginine-C 14 or P 32. AP1 became labeled first, followed by AP2, and AP3, in P 32 experiments. AP1 and often AP1 and AP2 were labeled with arginine-C 14. 5. 5. In several experiments, when AP1 was the only fraction labeled with arginine-C 14, AP2 became radioactive upon stimulation of the ABRM. A possibility of selective participation, of the three fractions, in muscle contraction is discussed.