Alanyl adenylate

The aminoacyl adenylates react rapidly with amino acids to yield peptides39 , under physiological conditions in aqueous solution at room temperature. At pHs higher than 7, the maximum is attained at pH 10 where the extent of the polymerization of peptides from alanyl adenylate is about 60 % 40). The aminoacyl adenylate in aqueous solution undergoes an intra- or inter-molecular rearrangement with the formation of 2 (3 )-aminoacyl ester of adenosine 40). 

Acidic proteinoid potentiates the active structure of lysine-rich proteinoid participating in forming microspheres in neutral buffer. Physical surface effects and providing micro condition in the microspheres could be surmised. Activation of amino acids generally requires acidic condition. Amino acids are activated by ATP and Mg2+ at pH 4-5 32 33). Aminoacyl adenylate anhydride and ester is formed preferentially from amino acid and adenylate imidazolide at pH 6.0J7). On the other hand, polycondensation of activated amino acids undergoes at pH values higher than 7. Peptides are formed from aminoacyl adenylate in basic buffer (the optimum pH is 10 for alanyl adenylate 40) from amino acid adenylate phosphoramidate and imidazole at pH 7.0 from N-(aminoacyl)-imidazole at pH 6-9 43). In this context, acidic and basic environments may be provided inside and/or on the surface of the microspheres composed of acidic and basic proteinoids in neutral buffer. Acidic micro condition suitable for the activation of amino acids and basic micro environment favorable for peptide formation from activated amino add may be provided. 

The P-alanyl dipeptides carnosine and anserine (A -methylcarnosine) (Figure 31-2) activate myosin ATPase, chelate copper, and enhance copper uptake. P-Alanyl-imidazole buffers the pH of anaerobically contracting skeletal muscle. Biosynthesis of carnosine is catalyzed by carnosine synthetase in a two-stage reaction that involves initial formation of an enzyme-bound acyl-adenylate of P-alanine and subsequent transfer of the P-alanyl moiety to L-histidine. 

Aminoacyl adenylates (296), which are formed from protein amino acids and ATP, act as acylating agents towards t-RNAs, acylating their terminal 3 -hydroxy groups. These charged tRNAs are then used in protein synthesis. Little is known about the reactivity of aminoacyl adenylates (296), and studies are now reported of a model compound, alanyl ethyl phosphate (297). As expected, hydrolysis in both acid and base involves attack at the C=0 group of (297) with departure of ethyl phosphate. Metal ions (Cu +, Zn +) were found to act as catalysts of the hydrolysis. 

---