Figure 1.
Figure 1 The complete pathway of the de novo biosynthesis of
BH[4]. The cofactor BH[4] is synthesized by only three enzymes,
namely CYH, PTPS and SR. The crystal structure of E.coli CYH was
recently solved by single isomorphous replacement and averaging
techniques. The enzyme complex, a decamer consisting of a
pentamer of tightly associated dimers, has perfect D[5] symmetry
and is doughnut-shaped with dimensions of 65 100
Å. The MIR-solved crystal structure of rat PTPS shows a
hexameric enzyme composed of a dimer of trimers with D[3]
symmetry. Each trimer forms a 12 -stranded antiparallel -barrel,
enclosing a basic pore with 6 -12 Å diameter. The crystal
structure of mSR completes the structural analysis of all three
enzymes involved in BH[4] biosynthesis, providing the essential
information for the interpretation of the complex biochemical
regulation of this pathway.
100
Å. The MIR-solved crystal structure of rat PTPS shows a
hexameric enzyme composed of a dimer of trimers with D[3]
symmetry. Each trimer forms a 12 -stranded antiparallel 
-barrel,
enclosing a basic pore with 6 -12 Å diameter. The crystal
structure of mSR completes the structural analysis of all three
enzymes involved in BH[4] biosynthesis, providing the essential
information for the interpretation of the complex biochemical
regulation of this pathway.