The activity of purified adenosine deaminase isolated from the gray an
d white matter of bovine brain was inhibited by chemical modification
of tryptophan residues with N-bromosuccinimide and photooxidation in t
he presence of trichloroethanol. Only two of six modified residues wer
e essential for activity of the enzyme. A preliminary kinetic study sh
owed that these essential. tryptophan residues are adjacent to the sub
strate-binding site of the enzyme.