232
G. L. CANTONI
Θ
R—CH 2 —0—P0 3 H 2 + H
+ + Enzyme
R—CH 2 —B' + Enzyme
Θ
Γ
© Ί
Enzyme + R—CH 2 —B^=£B + [ R—CH 2 —EnzymeJ
R—CH 2 —OH + H+ + Enzyme
R—CH 2 —XH + H
+ + Enzyme
FIG. 16.
NH 2
X ^
ΛΝΛ Ν/
H
I
β
CH—CH(OH)—CH(OH)—GH—CH 2 —S—CH 2 —CH 2 —CH(NH 2 )—COO-O
1
CH 3
+
^CONH 2
I t
N '
NH 2
1 !
(
25 )
JX>
Η·
Ν
J
CH—CH(OH)—CH(OH)—CH—CH 2 —S—CH 2 —CH 2 -CH(NH 2 )—COOI
.—o
1
+
^CONH 2
I ®
CH 3
fully understood. Thus with the DPNases the reaction with a number of
analogs of nicotinamide has been shown to be freely reversible (196,
198); with the thiaminase some reversibility could be demonstrated
from the pyridinium analogue but the equilibrium was very markedly
in favor of thiamine cleavage (199). Finally base exchange between Sadenosylmethionine and nicotinamide as postulated in Reaction 25
could not be demonstrated (174).