Effect of Polyamines on Isoleucyl‐tRNA Formation by Rat‐Liver Isoleucyl‐tRNA Synthetase

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Abstract
The effect of polyamines on rat‐liver isoleucyl‐tRNA formation was studied using isoleucyl‐tRNA synthetase purified by column chromatography successively on Sephadex G‐200, DEAE‐Sephadex A‐25, and tRNA‐Sepharose 4B. In the presence of 50 mM K+, isoleucyl‐tRNA formation was inhibited markedly by 1.5 mM or higher concentrations of Mg2+. However, the addition of spermine to the reaction mixture prevented the inhibitory effect of Mg2+. In the presence of 200 mM K+, the addition of spermine to the reaction mixture stimulated isoleucyl‐tRNA formation in the presence of Mg2+ concentrations from 0 to 5 mM. Although the effective concentration was different, spermidine exhibited a similar stimulative effect. The effective concentration of spermine required for stimulation was higher when larger amounts of tRNA were used. The stimulatory effect of isoleucyl‐tRNA formation by polyamines was shown to reflect on polypeptide synthesis. When formaldehyde‐treated poly (A, U) was used as messenger RNA, polypeptide synthesis from amino acids was stimulated by polyamines, but that from aminoacyl‐tRNAs was not stimulated by polyamines.