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Figure 5.
Figure 5 Catalysed reaction of SR: reductase and isomerase. SR
catalyses the sequential diketo reduction of PH[4] (6-pyruvoyl
tetrahydropterin) conducive to the formation of BH[4] via an
essential isomerization step of the mono-keto intermediates
(reactions 1 -3). For C2'-reduction of the 2' -mono keto
intermediate (reaction 4), an essential reorientation of the
substrate's side chain toward Tyr171 and NADPH can be proposed.
The reduction of the 2'-oxo function of PH[4] (reaction 5) is
presumably not catalysed by SR.
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