R NH 2 A 0 X "",lR' ~ 1~~I~sfer RyNH o HO X + ~ 11 R-C-N-R' H release ~ new peptide HO O \-R' X'" ~ A potential capture si te exploited by Kemp's group is the thiol function of aN-terminal cysteine residue. The O,N-acyl transfer occurs via a medium-size ring intermediate. Proximity effect, solvent effect, steric and stereoelectronic effects, all contribute to the success of the designed plan.
CH-NH 2 H 1 ~ / CH_COOe 2 + AMP (adenosine monophosphate) hippuric acid The ester linkage between the hydroxyl of the tRNA is a high-energy bond (because of the adjacent 2' -hydroxyl and cationic amino functions), so that the overall enzyme-catalyzed re action has a free-energy change dose to zero. Each amino acid has a specific tRNA moleeule and one specific aminoacyl-tRNA synthetase enzyme. In turn, each aminoacyltRNA synthetase enzyme will accept only its particular amino acid as a substrate.
A favorable entropic factor is involved since water molecules go es back to the "pool" of solvent. The last two associations are hydrophobie in nature. To summarize, the design of an artificial enzyme or receptor involves the construction of a molecular architecture or a distinct cavity complementary to a substrate that could be even more efficient if it could also resemble as closely as possible the transition state of an intermediate of the re action to be mimicked. In other words, the catalytic process to be mimicked would be facilitated if its transition state could be stabilized by specific receptor-substrate interactions.
Bioorganic Chemistry: A Chemical Approach to Enzyme Action by Hermann Dugas