Aspartate aminotransferase absorption spectra

Figure 14-9 Absorption spectra of various forms of aspartate aminotransferase compared with that of free pyridoxal phosphate. The low pH form of the enzyme observed at pH <5 is converted to the high pH form with pka 6.3. Addition of erythro-3-hydroxyaspartate produces a quinonoid form whose spectrum here is shown only 1/3 its true height. The spectrum of free PLP at pH 8.3 is also shown. The...

Absorption bands at 500 nm. With many PLP enzymes certain substrates and inhibitors cause the appearance of intense and unusually narrow bands at 500 nm. Such a band is observed with aspartate aminotransferases acting on eryf/zro-3-hydroxyaspartate (Fig. 14-9). This substrate undergoes transamination very slowly, and the 500-nm absorbing form which accumulates is probably an intermediate in the normal reaction sequence. A similar spectrum is produced by tryptophan indole-lyase acting on the competitive inhibitor L-alanine. Under the same conditions the... 

Fig. 45. Electronic absorption spectrum for carbamylated aspartate aminotransferase in the presence of pyridoxal-P (curve 1) and following the addition of aspartate to the latter (curve 2).

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