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The synthesis of a peptide, composed of fifty amino-acid residues, corresponding to positions 42-91 in ovine beta-lipotropin has been accomplished by the solidphase method. The preformed symmetrical anhydride and active ester coupling methods were used exclusively. The synthetic product was purified by gel filtration, carboxymethylcellulose chromatography, and partition chromatography on Sephadex G-50. Its lipolytic activity in isolated rabbit fat cells was about six times that of beta-lipotropin on a weight basis.

The synthesis of the n-hydroxysuccinimide ester of N-(2-nitro-4-azidophenyl)glycine (NAG) is described. This reacts with E. coli phe-tRNA(Phe) to yield the photoaffinity label NAG-Phe-tRNA(Phe). This peptidyl tRNA analogue binds correctly to the peptidyl site of the E. coli ribosome. The only significant covalent products found after irradiation of a peptidyl site bound NAG-Phe-tRNA(Phe)-70S-poly(U) complex are 50S proteins L11 and L18. After irradiation the complex can still bind [(3)H]Phe-tRNA to the amino acyl site and participate in peptide bond formation with the covalently attached NAG-Phe moiety. Alternatively, one can allow peptide bond formation to occur first, prior to photolysis. The reaction products are still L11 and L18. Hence, both of these two proteins appear to be centrally located at the peptidyl transferase center.