title: Neurofilament protein is phosphorylated in the squid giant axon.
abstract: We have observed the phosphorylation of neurofilament protein from squid axoplasm. Phosphorylation is demonstrated by 32P labeling of protein during incubation of axoplasm with [gamma-32P]ATP. When the labeled proteins are separated by SDS-polyacrylamide gel electrophoresis (SDS-PAGE), two bands, at 2.0 x 10(5) daltons and greater than 4 x 10(5) daltons, contain the bulk of the 32P. The 2.0 x 10(5)-dalton phosphorylated polypeptide comigrates on SDS-PAGE with one of the subunits of squid neurofilament protein. Both major phosphorylated polypeptides co-fractionate with neurofilaments in discontinuous sucrose gradient centrifugation and on gel filtration chromatography on Sepharose 4B. The protein-phosphate bond behaves like a phospho-ester, and labeled phospho-serine is identified in an acid hydrolysate of the protein. The generality of this phenomenon in various species and its possible physiological significance are discussed.
mesh_terms: D001369:Axons / Q000032:analysis*; D049832:Decapodiformes / Q000033:anatomy & histology*; D008970:Molecular Weight; D009419:Nerve Tissue Proteins / Q000032:analysis*; D009454:Neurofibrils / Q000032:analysis*; D010455:Peptides / Q000032:analysis; D010766:Phosphorylation
chemical_list: D009419:Nerve Tissue Proteins; D010455:Peptides