1994 PROGRAM Twentieth Annual
_  __  Symposium on
AM. P.M.
9:00 Registration and Coffee - Room 137. 12:15 Buffet Lunch, Faculty Club (Please return 0
Chemistry-Physics Building card by April 1, 1994 for reservations. Chemlstry
9:30 Wecome by Dr. David Watt, Vice Chancellor COSt $1000 to be paid at registration.)
fonResearch and Graduate Studies, 1:40 Dr. Robert R. Eady, University of Sussex
Umversrty of Kentucky - Room 139. . . . .
Ch , t Ph , B ,1 d The Role of Vanadium in Biological
emls ry- ys1cs 1 mg Nitrogen Fixation
9:40 Introductory Remarks - Mark Meier.
University of Kentucky Three related, but genetically distinct. nitrogenase l
_ _ _ . systems are known to be present in Azotobacter species. 0 e c 1 ar
9'45 Dr. Douglas C' Rees, California Institute Of One. which is found in all Ngfixing bacteria and has been
Technology _ . studied extensively for many years, is based on Q
The Structure and Function ofNitrogenase molybdenum and iron: at second [first isolated in 1986) B1010
The conversion of dinitrogen to ammonia during contains vanadium and ironzandathird (first isolated in
biological nitrogen xation is catalyzed by the nitro- 1988] appears to contain only iron. Which of these
genase enzyme system. Nitrogenase consists of two systems 18 expressed depends on the avallability of
component proteins, the iron [Fe) protein and the Mo and V to the organism. The results of studies on the
molybdenumiron [MoFe) protein. Threedimensional regulation of the expression of these alternative systems ,
structures of both proteins have been determined by by M0 and V and the structurefunction relationships of
Xray crystallography. The MoFeprotein is an 05232 V-nitrogenase. in comparison with Monitrogenase 0f
tetramer containing two different types of metal centers. Azotobacter WI be rev1ewed. '  '
the FeMocofactor and the P-cluster pair. while the . .
Fe-protein contains a single 4Fcz4S cluster symmetri 2:40 Discussron .
cally ligated by two identical subunits. Aspects of the . . _ . . . _ ,
nitrogenase mechanism. as well as general structural 250 D1." D3mtn Coucouvanls, UniverSIty 0f
similarities that exist between nitrogenase and other Michigan   t bl' h d . th f
complex electron transfer systems, will be explored. :yntlletlc Models ofthe Nitrogenase Fe/Mo/S CS a IS 6 In 6 memory 0
us er :
10:45 Discussion Anna A' Naff
1055 Dr William E Newton Vir inia Recent Xray structure determinations of the Fe/Mo
' Pol tech nic and StateUniEersit protein of nitrogenase revealed the structure of the ___
ProSIn'ng Ni trogenase Catalytic FYunction Fe / Mo / S active site. Neither the Fe453 nor the MoFe383 NITROGEN ASE;
. . . . subunits have precedents among synthetic clusters with
Through Ammo Add Substitutions biologically acceptable terminal ligands. In this lecture THE CHEMISTRY OF BIOLOGICAL
The nitrogenase complex consistsof a smaller Fe we will report on the first observation of catalytic NITROGEN FIXATION
protein.which acts as an ATPbinding, specific electron behavior by synthetic Fe/MO/S clusters that struc E B
donor to the larger 0.3133 MoFe protein, which contains turally. albeit partially. resemble the Fe/MO/S site of 4! 8 __
the substratebinding site. The MoFe protein contains nitrogenase. Some of these clusters are effective in the .2 E |
two types of prosthetic group: two Pcluster pairs, each catalytic reduction 0f hydrazine to ammonia in what E g 8 SPEAKERS
ofwhich consists oftwo [4Fe4S] clusters bridged by the COUld be the 1351 stage in nitrogen fixation. Reactivity .: *4 L0 , , , _
yS of two cysteinyls (Cys) and a likely disulfide bond: studies strongly implicate the Mo atom as the site directly 0 E g D1rn1tr1 N. COUCOlealllS
and two FeMo-cofactors {or M centers), each of which involved in the reduction of N3H4. These studies also 8 M Robert R_ Eady
has the composition, MoFe7S.){homocitrate). Our ap- suggest that the catalytic process likely occurs by a H 45 E . _
proach to assigning function to the individual prosthetic single metal site mechanism. POSSible pathways Of these 8 3 52: Wllham E- NCWtOII
groups is through sitedirected mutagenesis/gene- reactions will be presented E 7) 8 Douglas C. Rees
replacement techniques, then monitoring the conse t: 3-; no
quences of these substitutions. Correlated changes in 3150 Discussion a 3 E
EPR spectra and catalytic properties occur on substitu q; 3:: Monda A til 1 1 1994
tion of residues interacting with the FeMo cofactor, 4:00 Mixer - Room 137, Chemistry-Physics D D .3 Y, P 
indicating the intimate involvement of this prosthetic Building
group with the substratereducing site. Aworking model -
ofnitrogenase function based on these and other results DEpEirtmdllt Of ChemlStry
will be described. Un1vers1ty of Kentucky
11:55 Discussion Lexington, Kentucky 405060055