1. Transferase I from rat liver extracted with iso-octane binds significantly less aminoacyl-tRNA than the non-extracted enzyme. The original activity can be fully restored by the addition of cholesteryl 14-methylhexadecanoate. The binding capacity for GTP is not affected by the extraction. 2. In the presence of extracted transferase I the binding of aminoacyl-tRNA to ribosomes is decreased to 11–26% and the simultaneous binding of GTP to 32–43%. Cholesteryl 14-methylhexadecanoate induces a full reactivation of the extracted enzyme in both respects. 3. Extracted complexes A (aminoacyl-tRNA–GTP–transferase I) become bound to ribosomes to the same extent as the corresponding non-extracted preparations. 4. It is concluded that cholesteryl 14-methylhexadecanoate interacts with the binding site of transferase I for aminoacyl-tRNA and secondarily with that for GTP. It does not affect the binding site for ribosomes.
