Synthetic Peptide Models of Enzyme Active Sites. I. cyclo-Glycyl-L-histidyl-L-serylglycyl-L-histidyl-L-seryl

Histidine‐containing cyclic dipeptides as catalysts in the hydrolysis of carbonic acid p‐nitrophenyl esters

“…(2). With imidazole-containing peptides employed in the present investigation, the same mechanism was shown to operate (see Results).…”

Halosugar nucleosides. II. Iodination of secondary hydroxyl groups of nucleosides with methyltriphenoxyphosphonium iodide

“…of the phenoxyphosphonium ion from 3 as diphenyl methylphosphonate and formation of the 02,3'-cyclothymidine (4). Subsequent opening of 4 by iodide then gives the observed erythro iodide (5). Similar interventions of 02,3'-cyclonucleosides have been invoked to explain retention of configuration during displacement of 3'-0-mesyl functions by halides,6-6 azide,7 carboxylate,8 and imide9 ions.…”

“…In addition to unreacted 8a, the major product was an extremely polar material that was shown to be a monoanion by paper electrophoresis at pH 3 or 7.6. Following hydrolysis of the p-nitrobenzoyl group from this substance a mixture of uridine 17 Hz) 22 5.87 (d, 8 Hz) 7.81 (d, 8 Hz) 6.29 (d, 5 Hz) 4.1-4.5 (m) 3.85 (m) 1.14 (d, 17 Hz) a Determined in D20 at 100 MHz relative to an internal standard of 2,2-dimethyl-2-silapentane 5-sulfonate. 6 The C2.H,Cg'H, and , are usually superimposed upon each other and upon the HDO signal.…”

Catalytic hydrolysis by synthetic polymers

“…Interestingly, pH-rate profiles for copoly (His, Glu) and copoty (His, Asp) were bell-shaped with maxima at pH 6.9 in phosphate buffer and at pH 7.4 in barbital buffer. Sheehan and co-workers prepared a pentapeptide, L-Thr-L-AIa-L-Ser-L-His-L-Asp as an esterase model, from a viewpoint that three amino acids (serine, histidine and aspartic acid) are involved at the active site (131,132). The rate constant for the pentapeptide 11, 1.5 M -1 sec -1 (pH 7.73, 25.5 °) is greater than 0.25 M -1 sec -1 for tripeptide L-Gly-L-His-L-Ser and 0.3 M -l sec -1 for imidazole.…”