Polyamines metabolically labeled two cellular proteins in fibroblasts isolated from chick embryos

A hypusine-containing protein (Mw=18,000) has been reported to be present in all mammalian cells examined. The formation of the unusual amino acid residue in this 18,000-dalton protein is due to a posttranslational modification of lysine residue by spermidine. To search for an abundant source for the purification of this protein, they have examined possible existence of this protein in chick embryos using metabolical labeling method. Metabolical labeling of chick embryo fibroblasts prepared from the Day 11 embryos by [2,3-3H]putrescine resulted in two prominently labeled protein bands as shown by SDS-PAGE and fluorography. The apparent molecular weights of the labeled proteins were 20,000- and 18,000-daltons. Two-dimensional gel analysis indicated that the 20,000-dalton protein had a pI of 5.5 and the 18,000-dalton protein exhibited isoform structures with pI values ranging from 4.6 to 5.1. Peptide map analysis showed that the 18,000-dalton protein from chick embryos was identical to the 18,000-dalton protein isolated from mouse neuroblastoma cells. The purification procedure that they have developed for mouse neuroblastoma 18,000-dalton protein was found to be also applicable in isolating the 18,000-dalton protein from chick embryos. Both the 18,000- and the 20,000-dalton proteins in chick embryos were enriched after Cibacron-Blue column and omega-diaminooctyl-agarose column chromatography