Characterization of recombinant Porphyromonas gingivalis serine palmitoyl transferase (SPT). (A) Absorption ultraviolet-visible spectrum of PLP-dependent (pyridoxal-5′phosphate) P. gingivalis SPT. Upon addition of L-serine, the enzyme (20 μM) converts from the internal aldimine to the external aldimine form, performed in 20mM potassium phosphate, 250mM NaCl, pH 7.5, at 25 °C. Solid line (0mM L-serine) or dashed lines in the presence of 0.1mM to 100mM L-serine. (B) Analysis of L-serine binding to C-terminal PgSPT by monitoring the change in absorbance at 425 nm. (C) Michaelis-Menten kinetic analysis of SPT with substrates L-serine (0.1 to 100 mM) and palmitoyl-CoA (250 μM) with 1μM enzyme, 100mM HEPES, pH 7.0, 250mM NaCl, and 0.2mM DTNB and measured spectrophotometrically at 412 nm. (D) The concentration of L-serine (20 mM) with different palmitoyl-CoA concentrations (1 to 1000 μM). All data are plotted as mean readings ± 2-SD error bars.