Cadmium-substituted alcohol dehydrogenase
Together with Lars Hemmingsen from Copenhagen, I developed a procedure
for the calculation of electric field gradients of cadmium complexes [18].
This method was then used to interpret measurements performed by perturbed
angular correlation of gamma-rays (PAC) on alcohol dehydrogenase [24].
Structures of the Cd-substitued enzyme with various ligands and coenzymes
were estimated with COMQUM and field gradients were calculated by our method.
The results are impressive: the calculations reproduce electric field gradients
of seven measurements with an average error of only 0.11 a.u. (9 %), and
we reinterpret several of the experiments. The results show that the enzyme
is four-coordinate in all examined complex and that the measurements most
likely give the first experimental evidence for Glu-68 coordinating to
the cadmium ion. Such a coordination has now been confirmed by the crystal
structure of human alcohol dehydrogenase [J. Mol. Biol. 265(97)330], another
encouraging success for our COMQUM calculations. The calculations also
indicated that the semiempirical method normally used for the interpretation
of PAC measurements could be improved. We have therefore also suggested
how the method may be improved using quantum chemical calibrations [35].