Studies on the enzymatic hydrolysis of amino acid carbamates

Several commercially available enzymes were tested for their ability to hydrolyze amino acid carbamates. No activity was found with pig liver esterase, the hydantoinase from Pseudomonas fluorescens DSM 84, or the urease from jack beans. A stereoselective cleavage of the carbamyl group yielding L-amino acids was observed by acylase and acetylcholinesterases from bovine and human erythrocytes. Racemic mixtures of N-(methoxycarbonyl)-DL-alanine, N-(ethoxycarbonyl)-DL-alanine, and the corresponding valine carbamates are hydrolyzed to L-alanine and L-valine, respectively, by acylases leaving the D-amino acid carbamates unchanged. The lysine carbamates were not hydrolyzed by acylases. In contrast only the methoxycarbonyl amino acids were split by acetylcholinesterases, which, however, also cleave alpha, epsilon-(N-methoxycarbonyl)-DL-lysine stereoselectively at the alpha position, yielding epsilon-N-methoxycarbonyl-L-lysine. The optimum pH for enzymatic activity of hog kidney acylase was 7.5 and a Km value of 8.2 mM for N-(methoxycarbonyl)-DL-alanine was determined. For the acetylcholinesterases the reaction rate reaches an optimum between pH 7.5 and 8. The Km value was 68 mM for N-(methoxycarbonyl)-DL-alanine.