Using photo
affinity l
abeling, we h
ave identified
a region inm
amm
ali
an f
arnesyl-proteintr
ansfer
ase (FPT
ase) involved in substr
ate recognition. Thephotol
abel used (Compound 1) is
a peptidecont
aining the photo
active
amino
acid
p-benzoylphenyl
al
anine(Bp
a). Upon exposure to UV light,Compound 1 inhibits FPT
ase
activity in
a time-
andconcentr
ation-dependent m
anner. Photoinhibition ofFPT
ase
activity by Compound 1 is prevented by
adding H-R
as to there
action mixture, indic
ating th
atl
abeling is t
argeted to the enzyme
active site. We used peptidem
apping by HPLC, Edm
an sequencing,
and m
atrix-
assisted time-of-flight (MALDI-TOF) m
ass spectrometry toidentify the site of inter
actionwith r
adiol
abeled Compound 1. These experiments indic
ate th
at
aspecific region of the
![](/im<font color=)
ages/gifch
ars/
alph
a.gif" BORDER=0> subunit of theenzyme, Asp110-Arg112, is involved in substr
ate binding
and suggestth
at Glu111 is likely to be theresidue cov
alently modified by the photo
affinity l
abel. Sequence
alignments between ye
ast
and m
amm
ali
anFPT
ases reve
al th
at Glu111 is conserved. The implic
ations of thisfinding
are discussed in light of previousmut
agenesis studies on FPT
ase.