FIG. 3.

Lysine decarboxylase enzyme characterization. His-tagged LdcA protein was purified from E. coli. Enzyme-catalyzed lysine decarboxylation was assayed by measuring the liberated ¹⁴CO₂ as previously described in Materials and Methods. (A) Kinetics studies exhibiting cooperative substrate activation pattern with the corresponding Hill slope plot. Assays with increasing lysine concentrations were performed at pH 8.5, 37°C. (B and C) Optimal conditions for lysine decarboxylation were tested as described in Materials and Methods. (D) Cold polyamines or amino acids (5 mM) were added into the standard reaction mixture to test for allosteric effects.