H. Deng et al., CHARACTERIZATION OF HYDROGEN-BONDING IN THE COMPLEX OF ADENOSINE-DEAMINASE WITH A TRANSITION-STATE ANALOG - A RAMAN-SPECTROSCOPIC STUDY, Biochemistry, 37(14), 1998, pp. 4968-4976
The Raman spectra of purine ribonucleoside as well as a stable model c
ompound (1-methoxyl-1,6-dihydropurine ribonucleoside), free in solutio
n and bound into its complex with adenosine deaminase (ADA), have been
studied by Raman difference spectroscopy. Using purine riboside analo
gues labeled with (15)N1 or (13)C6 and the theoretical frequency norma
l-mode analyses of these molecules using ab initio quantum mechanic me
thods, we have positively identified many of the Raman bands in the en
zyme-bound inhibitor. The spectrum of the enzyme-bound inhibitor is co
nsistent with the enzyme-catalyzed hydration of the purine base to yie
ld 1-hydroxyl-1,6-dihydropurine ribonucleoside, as suggested earlier b
y X-ray crystallographic studies. In addition, the Raman data and subs
equent vibrational analyses show that the binding-induced Raman spectr
al changes of the inhibitor can be modeled by the formation of a stron
g hydrogen bond to its N1-H bond. This hydrogen bond, apparently betwe
en the N1-H of the inhibitor and the O delta 1 of Glu217 in ADA, cause
s a substantial N1-H bending frequency increase of about 50-100 cm(-1)
compared to its solution value, and this results in an estimated enth
alpy of the hydrogen bond of 4-10 kcal/mol. The relationship of transi
tion state stabilization in the catalytic strategy of this efficient e
nzyme to such a bonding pattern is discussed.