Aminoacyl-transferase II,

Honjo, J., Nishizuka, Y., Hayaishi, O., and Kato, I. (1968) Diphtheria toxin-dependent adenosine diphosphate ribosylation of aminoacyl transferase II and inhibition of protein synthesis. J. Biol. Cbem. 243, 3553-3555. 

Studies with ribosomes indicated that, in contrast to experiments with microsomes, the purified transferring enzyme described above failed to catalyze aminoacyl transfer (Tablem) however, the crude pH 5 Supernatant was active with both particle preparations. As described in Table IV, when the incubations with purified enzyme (transferase I) were supplemented with the dialyzed deoxycholate-soluble microsomal extract (transferase II) obtained during the isolation of ribosomes (Figure 1), transferring activity was restored (6, 7). Glutathione was also... 

Previous studies demonstrated that GTP was the only essential nucleotide in the aminoacyl transfer reaction (2, 10, 21, 22). The effect of varying concentrations of GTP on this reaction is presented in Figure 6. Maximum incorporation was obtained with as little as 0.05 jLimole of GTP per ml. in incubations with transferase I and soluble transferase n. When microsomal transferase II was used, the requirement for... 

The aminoacyl transfer reaction, one of the latter stages in protein synthesis, involves incorporation of amino acids from soluble ribonucleic acid-amino acid into ribosomal protein. This reaction requires guanosine triphosphate and a soluble portion of the cell. Evidence has been obtained with rat liver preparations that aminoacyl transfer is catalyzed by two protein factors, aminoacyl transferases (or polymerases) I and n, which have been resolved and partially purified from the soluble fraction. Transferase II activity has also been obtained from deoxycholate-soluble extracts of microsomes. With purified transferases I and n, incorporation is observed with relatively low levels of GTP its sulfhy-dryl requirement is met by a variety of compounds. The characteristics of this purified amino acid incorporating system, in terms of dependency on the concentration of its components, are described. 

Figure 5. Dependence of aminoacyl transfer on varying concentrations of transferases I and II...

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