Figure 28-17 Intermediate in the synthesis of tryp tophan. PLP (green)on a p chain o tryptophan synthetase forms a Schiff base with serine, which is then dehy H2C drated to give the schiff base of aminoacrylate (red). This enzyme C-C bound intermediate is attacked by indole, the product of the partial NH reaction catalyzed by the a subunit, to give tryptophan CH O2POH2C O CH 3
Serine c99c90 Enzyme alone Serine and indole 450 500 550 Wavelength(nm) Fi gure 8-10 Fluorescence intensity of the pyri- doxal phosphate group at the active site of tryptophan synthetase changes upon addition of serine and indole the substrates
ACTIVE SITES OF ENZYMES HAVE SOME COMMON FEATURES The active site of an enzyme is the region that binds the substrates(and the prosthetic group, if any) and contains the residues that directly partic. ipate in the making and breaking of bonds. These residues are called the catalytic groups. Although enzymes differ widely in structure, specificity, and mode of catalysis, a number of generalizations concerning their ac- tive sites can be stated
Common Features of the Active Sites of Enzymes The active site takes up a relatively small part of the total volume of an enzyme Model of myoglobin at high resolution Only the a carbon atoms are shown. The heme group is shown Figure 35-10 in red, and two key Structure of an ATPase fragment histidine residues in derived from hsc70, a cytosolic heat- green. [After R.E. shock protein. ADP (red)is bound in Dickerson. In The he cleft between the two domains Proteins, vol. 2. 2nd (yellow and blue).[Drawn from ed. H. Neurath, ed lats. pdb. K.M. Flaherty, (Academic Press C. DeLuca-Flaherty, and D B. McKay 1964),p.634. Naue346(1990):623
Common Features of the Active Sites of Enzymes