3. The spectroscopic characteristics of many enzymes and substrates change upon formation of an Es complex These changes are particularly striking if the enzyme contains a colored prosthetic group. Tryptophan synthetase, a bacterial enzyme that contains a pyridoxal phosphate prosthetic group, affords a nice illustra- tion c subunit Indole-3-glycerol phosphate indole glyceraldehyde 3-phosphate Indole +serine Ba subunit, tryptophan+H2O