Spermine specifically inhibits the phosphorylation of an 11,000-dalton nuclear protein in various cultured mammalian cell lines

Characterization of an arginine-specific protein kinase tightly bound to rat liver DNA

A new protein kinase has been characterized among the proteins tightly bound to rat liver DNA and released by DNase I and RNase A treatment. This enzyme was separated by gel filtration from this released material. Its apparent molecular mass was found to be 34 kDa and it is made of a single unit. The main characteristic of this protein kinase is that it is arginine-specific. Isolation of phosphoarginine required the use of proteolytic enzymes at alkaline pH since the phosphate bond is highly acid-labile. This protein kinase is able to autophosphorylate and to phosphorylate a single chromosomal protein of 11 kDa also tightly bound to DNA. It uses ATP and dATP as phosphate donors and is cAMP-independent. Its optimal activity requires Mn2+ ions. Vanadate, spermine and heparin have no effect on its activity.

Polyamines stimulate endogenous protein phosphorylation in thyroid cytosol

The polyamine, spermine (1-5 mM), when added to rat thyroid cytosol, increases the phosphorylation of a 107 kDa protein 4-fold as analyzed by sodium dodecyl sulfate polyacrylamide gradient gel electrophoresis (SDS-PAGE) and autoradiography; spermidine was less effective and putrescine was without effect. Sodium chloride, when tested at equivalent ionic strengths (4-40 mM), did not reproduce the effects of spermine. In addition to stimulating the phosphorylation of a 107 kDa protein, spermine had an apparent biphasic effect on the phosphorylation of 88 and 65 kDa proteins; maximum stimulation of approximately 60-70% was observed at 0.5-2 mM. Both basal and spermine-stimulated protein phosphorylation patterns were identical whether [gamma-32P] ATP or [gamma-32P] GTP was used as phosphate donors. Heparin (1 microgram/ml) reduced spermine-stimulated phosphorylation of the 107 kDa protein by 64%. Phosphorylation of a 107 kDa protein was not restricted to rat thyroid as spermine was found to augment the phosphorylation of 107 kDa protein(s) in mouse and beef thyroid cytosol preparations.