Composition of amino acid phosphates in phosphorylated G-actin of rabbit skeletal muscle

In our experiments the phosphorylation of actin was studied. Similar investigations have been published in the literature, however very long incubation time was applied in these studies and even so a low incorporation of phosphate concentration was found. The present phosphorylation experiments were performed using short incubation periods as usual in our myosin investigations and was characterized by an unexpectedly high phosphate saturation. We suggest that in suitable incubation medium the nucleotide- and phosphate-free actin prepared by using phosphate- and ATP-free solutions takes only 1 minute to become saturated, while in its peptide chain a N-P bond type acid labile phosphate is formed. On maximum saturation 9 M P-arginine, 0.4 M P-histidine and some minor phosphorylated derivatives can be observed. After a longer period of incubation, with a lower incorporation of phosphate (3 mol P) a more stable phosphorylated actin is formed. As a result of preparation and gel filtration a dimer and a monomer form of actin can be obtained. Both of them exhibit the basic properties of actin (polymerization, myosin-ATPase activation) and the phosphate incorporation described in this paper.