BIOMIMETICALLY ACTIVATED AMINO-ACIDS - CATALYSIS IN THE HYDROLYSIS OFALANYL ETHYL PHOSPHATE

Alanyl ethyl phosphate (1) is an activated derivative of alanine that is functionally related to the corresponding aminoacyl adenylate, the initial activated amino acid intermediate in protein biosynthesis. To establish the inherent reactivity of these species, the kinetic parame ters for hydrolysis of alanyl ethyl phosphate in water at 25 degrees C were determined. There is catalysis by acid (k = 4 x 10(-4) M(-1)s(-1 )) and base (k = 1.7 M(-1)s(-1)) along with two pH-independent process es (k = 3 x 10(-5) and 1.6 x 10(-3) s(-1)) that are connected as a kin etic titration curve of the amino group of alanyl ethyl phosphate (pK( a) = 7.8). The results are consistent with mechanisms proceeding via a ddition to the carbonyl of water or hydroxide with proton migrations. Reaction with methanol is slower than reactions with water while react ion with 2-propanol leads to complex products. In solutions sufficient ly concentrated for P-31 NMR analysis, alanyl ethyl phosphate also und ergoes reactions that produce alanylalanine and other condensation pro ducts. Metal ions catalyze the hydrolysis reactions through complex fo rmation. Cupric and zinc ions are most effective (similar to 100-fold larger rate constant than water: association constants > 100 M-1) with magnesium and calcium forming weaker and less reactive complexes. The se results show that aminoacyl alkyl phosphates are sufficiently stabl e to be used in water and that metal ions can facilitate their reactio ns. Improved catalysts will be needed to facilitate biomimetic process es such as aminoacylation of t-RNA.