Transamination reaction of hydrophobic pyridoxal with an α-amino acid in functionalized bilayer vesicles: co-operative catalysis by the imidazolyl group and copper(II) ions

Abstract

1-(N,N-Dihexadecylcarbamoylmethyl)-2-methyl-3-hydroxy-4-formyl-5-hydroxymethylpyridinium chloride (PL+2Cls) undergoes a transamination reaction with L-phenylalanine in single-walled bilayer vesicles formed from two different peptide lipids (N+C5Ala2C16 and N+C5His2CI6); co-ordination of copper(ii) ion to the Schiff-base intermediate results in a marked rate acceleration.

Artificial Enzymes

“…The other half-transamination, transformation of an α-amino acid to the corresponding α-keto acid, was also examined kinetically by employing the catalytic bilayer membranes composed of a peptide lipid ( 31 or 32 ) and a hydrophobic pyridoxal derivative ( 35a , 36a , or 37a ). , In the absence of metal ions, the reaction of l -phenylalanine proceeded through fast equilibrated formation of the aldimine Schiff base with the pyridoxal derivative ( 37a ), followed by much slower conversion into the pyridoxamine derivative ( 37b ) and β-phenylpyruvic acid. The rate-determining step in the overall reaction is the isomerization of the aldimine to the corresponding ketimine, since the accumulation of the ketimine species was not observed to any detectable extent during the reaction.…”