FIGURE 4.

Spectroscopic and kinetic monitoring of the aminoacrylate intermediate formed in the presence of cysteine. A, difference spectra ((CBS + cysteine) − CBS) obtained following rapid mixing of CBS with cysteine in 100 mm HEPES (pH 7.4) at 24 °C. The spectra were acquired every 2 s following mixing of 60 μm CBS with 50 mm cysteine. The internal aldimine has an absorption maximum at ∼406 nm, and upon addition of serine, it rapidly converts to the aminoacrylate intermediate with an absorption maximum at 465 nm. B and C, dependence of the apparent rates for the disappearance of the internal aldimine (B) and the formation of the aminoacrylate intermediate (C) on the concentration of cysteine. Insets, dependence of the absorbance changes at 406 and 465 nm, respectively, on cysteine concentration at 0.3 s after mixing.