FIGURE 5.

Spectroscopic and kinetic monitoring of the conversion of the aminoacrylate intermediate in the presence of homocysteine. A, difference spectra ((CBS-aminoacrylate + homocysteine) − CBS-aminoacrylate) obtained following rapid mixing of preformed CBS-aminoacrylate with homocysteine in 100 mm HEPES (pH 7.4) at 24 °C. To obtain the spectra, 60 μm CBS was premixed with 25 mm serine and then mixed with 30 mm homocysteine The spectra were recorded every 2 s. Addition of homocysteine resulted in the disappearance of the aminoacrylate intermediate (320 and 465 nm) and the re-formation of the internal aldimine with an absorption maximum at ∼406 nm. B, dependence of the apparent rates for disappearance of the aminoacrylate intermediate on the concentration of homocysteine.