Spermidine is bound to a unique protein in early sea urchin embryos.

Abstract

Spermidine is rapidly taken up and becomes bound to protein during the very early hours of sea urchin embryogenesis. During the first 6 hr after fertilization of freshly obtained sea urchin eggs (Strongylocentrotus purpuratus), which are incubated in the presence of exogenous 13H]-spermidine, up to 7% of the total cell-associated spermidine appears uniquely as spermidine. bound in macromolecular form. This unique protein containing spermidine migrates as a single radioactive band in gel electro phores It has a Mr of :30,000 and is readily distinguishable from the protein initiation factor eIF-4D, which has a Mr of 18,000, the only other identifiable protein known to date to be posttranslationally modified by polyamines.In very early sea urchin (Strongylocentrotus purpuratus) embryogenesis we have discovered a protein containing intact, covalently bound spermidine. Putrescine, spermidine, and spermine, collectively referred to as the parent polyamines, are essential for the life of a cell and their intracellular concentrations are elevated during rapid cell division and growth (1-3). In addition, agents known to interfere with polyamine levels and metabolism block growth and differentiation (4). Yet, until recently, it has been difficult to assign particular roles to these small aliphatic amines, which are the most abundant endogenous cellular cations. The finding of hypusine, a polyamine metabolite, as a covalent component of the eukaryotic protein translation initiation factor eIF-4D was, to our knowledge, the first example of a polyamine derivative in a specific macromolecule (5). We now find that intact spermidine is present as a posttranslational modification of a unique protein with a Mr of =30,000, an example of an intact polyamine bound covalently to a specific macromolecule.The cellular uptake of [3H]spermidine by freshly fertilized sea urchin eggs and its distribution between the trichloroacetic acid (CCl3COOH)-soluble and CCl3COOH-insoluble fraction of cells are presented in Fig.

Changes in Polyamine Contents Development of the Frog, Microhyla ornata

“…In the free form, putrescine is the major polyamine while in the protein conjugated state, spermidine was the predominant form. Spermidine has been shown to be rapidly taken up and covalently bound to a specific protein during early hours of sea urchin embryogenesis (3).…”

Probing the transglutaminase-mediated, posttranslational modification of proteins during development

“…Although for the earliest 2-cell specimen (see panel I in Figure 3) a case could be made for the preferential labeling of 90K and 162K polypeptides, it is clear that our results do not support the claim for the existence of a "unique" transglutaminase-sensitive protein of about 30K in size. That conclusion was reached by Canellakis et al (1985), who, following our work with [14C]putrescine (Cariello et al, 1984), employed [3H]spermidine to identify posttranslational products of transglutaminase in fertilized sea urchin eggs without, however, proving that the polyamine was actually incorporated into 7-glutamyl residues in proteins.…”