Hydrophobic effects on rates and substrate selectivities in polymeric transaminase mimics

The amination of ketoacids to amino acids by pyridoxamine is greatly accelerated when the pyridoxamine is covalently linked to polyethylenimine carrying N-methyl and N-lauryl groups. Michaelis-Menten kinetics is seen with all substrates, from which the effect of the lauryl groups and the methyl groups can be determined with respect to the strength of binding of the substrate and the rate constant k2 within the complex. The polyamine catalyzes the reaction using acid and base groups, the lauryl groups increase k2 by producing a nonpolar medium in which the reaction occurs, and the lauryl groups promote binding of hydrophobic substrates. The result is that the amination of indolepyruvic acid to produce tryptophan is accelerated by 240000-fold.