An enzymatic method for radiolabeling vertebrate vitellogenin.

Phosphoprotein kinases from Xenopus and chicken liver have been purified and these enzymes have been used to label Xenopus vitellogenin, a phosphoprotein, to high specific activity with [gamma-32P]ATP. The enzymes were isolated by (NH4)2SO4 fractionation followed by chromatography on DE-52 cellulose and phosphocellulose. This procedure resulted in greater than 20,000-fold enrichment for the enzymes. Both enzyme preparations were used to selectively label vitellogenin in the serum of estrogen-treated animals. Thus, isolation of the vitellogenin prior to radiolabeling was not necessary. The [32P]vitellogenin labeled in situ was incorporated by oocytes at a rate similar to [32P]vitellogenin labeled in vivo, was translocated to the yolk platelets, and was correctly processed into the yolk proteins.