ABSTRACT
S-peptide (residues 1--14) analogues in which the active histidine-12 residue is replaced by Npi-methyl-L-histidine, Ntau-methyl-L-histidine and beta-(pyrid-3-yl)-L-alanine were synthesized and tested for their capacity to bind to S-protein and to activate it. The results show that both imidazolyl nitrogen atoms are required for optimal catalytic functioning, Ntau being essential to the catalytic reaction itself, Npi playing a role in keeping the imidazole ring in the correct position.
Subject(s)
Histidine , Ribonucleases , Catalysis , Enzyme Activation , Nitrogen , Protein Binding , Protein ConformationSubject(s)
Ribonucleases , Animals , Cattle , Glycine , Histidine , Imidazoles , Kinetics , Pancreas/enzymology , Peptides/chemical synthesis , Peptides/metabolism , Ribonucleases/metabolismABSTRACT
In our investigations on the effect of replacement of histidine by homohistidine (1) on the biological activity of some peptide-hormones, relatively large quantities of Boc-homohistidine were required. Homohistidine being difficult to synthesize, it was essential to find an effective way of introducing the Boc-group. In the past, many syntheses of Boc-histidine were reported (2-6), none of which proved to be quite satisfactory. However, by modifying the procedure of Flouret et al. (6) a convenient method resulting in a high yield of Boc-histidine and Boc-homohistidine was found.
