Inhibition of rat heart ornithine decarboxylase by basic polypeptides

Purified and partially purified ornithine decarboxylase (ODC) from rat heart was inhibited by basic polypeptides in vitro. Poly-L-arginine, the most effective, was inhibitory at a concentration as low as 0.1 microgram/ml; protamine and histone clearly inhibited ODC at concentrations higher than 2 micrograms/ml, but poly-L-lysine was less effective. The ability to inhibit ODC appeared to correlate with the arginine-residue content of basic polypeptides. The inhibition effect could be decreased by increasing substrate concentration and ionic strength.