Kjell Håkansson

Structure of native and apo carbonic anhydrase II and structure of some of its anion-ligand complexes.

In order to obtain a better structural framework for understanding the catalytic mechanism of carbonic anhydrase, a number of inhibitor complexes of the enzyme were investigated crystallographically. The three-dimensional structure of free human carbonic anhydrase II was refined at pH 7.8 (1.54 A resolution) and at pH 6.0 (1.67 A resolution). The structure around the zinc ion was identical at both pH values. The structure of the zinc-free enzyme was virtually identical with that of the native enzyme, apart from a water molecule that had moved 0.9 A to fill the space that would be occupied by the zinc ion. The complexes with the anionic inhibitors bisulfite and formate were also studied at neutral pH. Bisulfite binds with one of its oxygen atoms, presumably protonized, to the zinc ion and replaces the zinc water. Formate, lacking a hydroxyl group, is bound with its oxygen atoms not far away from the position of the non-protonized oxygen atoms of the bisulfite complex, i.e. at hydrogen bond distance from Thr199 N and at a position between the zinc ion and the hydrophobic part of the active site. The result of these and other studies have implications for our view of the catalytic function of the enzyme, since virtually all inhibitors share some features with substrate, product or expected transition states. A reaction scheme where electrophilic activation of carbon dioxide plays an important role in the hydration reaction is presented. In the reverse direction, the protonized oxygen of the bicarbonate is forced upon the zinc ion, thereby facilitating cleavage of the carbon-oxygen bond. This is achieved by the combined action of the anionic binding site, which binds carboxyl groups, the side-chain of threonine 199, which discriminates between hydrogen bond donors and acceptors, and hydrophobic interaction between substrate and the active site cavity. The required proton transfer between the zinc water and His64 can take place through water molecules 292 and 318.

Structure of cobalt carbonic anhydrase complexed with bicarbonate

The three-dimensional structure of a complex between catalytically active cobalt(II) substituted human carbonic anhydrase II and its substrate bicarbonate was determined by X-ray crystallography (1.9 A). One water molecule and two bicarbonate oxygen atoms are found at distances between 2.3 and 2.5 A from the cobalt ion in addition to the three histidyl ligands contributed by the peptide chain. The tetrahedral geometry around the metal ion in the native enzyme with a single water molecule 2.0 A from the metal is therefore lost. The geometry is difficult to classify but might best be described as distorted octahedral. The structure is suggested to represent a water-bicarbonate exchange state relevant also for native carbonic anhydrase, where the two unprotonized oxygen atoms of the substrate are bound in a carboxylate binding site and the hydroxyl group is free to move closer to the metal thereby replacing the metal-bound water molecule. A reaction mechanism based on crystallographically determined enzyme-ligand complexes is represented.

The structure of human carbonic anhydrase II in complex with bromide and azide

The three‐dimensional structure of human carbonic anhydrase II complexed with azide and with bromide was investigated crystallographically. Both of these non‐protonated inhibitors replace the zinc and the ‘deep’ water, two catalytically important water molecules in the active site of the molecule. Both the azide and the bromide ions bind in a distorted tetrahedral manner 0.4 and 1.1 Å from the zinc water position, respectively, but are in close contact (2.0 and 2.6 Å, respectively) with the zinc ion.

Dedicated accelerator and microprobe line

Abstract The development of a dedicated facility for nuclear microprobe analysis and the experiences from using it are discussed. The general properties of the present Lund nuclear microprobe will be described and the advantages of using a dedicated accelerator discussed.

The structure of a complex between carbonic anhydrase II and a new inhibitor, trifluoromethane sulphonamide.

It has recently been shown that aliphatic sulphonamides are good inhibitors of carbonic anhydrase (CA) provided that the pK of the sulphonamide is low. We have determined the structure of the complex between CAII and CF3SO2NH2 by X‐ray crystallographic methods. The nitrogen of the sulphonamide is bound to the zinc ion of the enzyme in the usual manner. The other parts of the inhibitor show a different mode of binding from aromatic sulphonamides since the trifluoromethyl group is bound at the hydrophobic part of the active site instead of pointing out from the active site. It should be possible to design new inhibitors specific for the different isoenzymes, starting from the present structure.

A new design for the low-energy optics of the Lund Pelletron accelerator

Abstract Several improvements have been implemented on the low-energy side of the Lund 3UDH Pelletron tandem accelerator. We report on the use of an ANIS sputtering source, the installation of a new injector with two legs and the rebuilding of the low-energy optics between sources and accelerator. New lenses have been placed at optimuum positions which, together with a higher pump capacity. increased the beamtransmission. Angular misalignment of the beam has been minimized by repositioning steerers and profile monitors.

Clinical useful quantities of [18F]fluoride produced by 6 MeV proton irradiation of a H2 18O target

Abstract Routine production of [ 18 F]fluoride has been carried out by 6 MeV proton irradiation of H 2 18 O water using a small-volume silver target vessel. By optimizing the target design, a 120 min irradiation of 600 μl 97% enriched [ 18 O]H 2 O at a beam current of 10 μA gives a practical yield of 5700±80 MBq (154±2 mCi). The produced [ 18 F]fluoride has been used for no-carrier-added synthesis of 2- 18 FDG.

Some improvements of the Pelletron accelerator in lund

Abstract Several improvements that have been implemented in the Pelletron system are described. The main components are protective automatically closing valves at each end of the accelerator tank, pick-up wheels and corona point supports of a new design, and valves in the stripper housing. These modifications result in improved operation reliability and a minimum of service interruptions.

The charge state distribution of a carbon beam measured at the lund pelletron accelerator with the newly installed terminal pumping system in use

Charge state distributions for (12) C and C-13 ions have been measured at the Lund Pelletron tandem accelerator for the N-2 gas stripper with a newly installed terminal pumping system in use. A comparison of the results obtained for the ion energies between 1.5 and 2.8 MeV with the foil stripper and the gas stripper without terminal pumping demonstrates the great improvement of the stripping process achieved with the new terminal pumping

An improved charge transport system for the Pelletron accelerator in Lund

Abstract Several improvements have been implemented in the chain charge transport system of a Pelletron. The main new components are a modified support at ground for the chain accessories, a new power supply for the chain motor, including the possibility of variable chain speed, and pickup rings to monitor the relative amount of charge on individual cylinders of the chain. These modifications, together with the installation of a second chain, have resulted in improved operational reliability, a much smoother startup of the chain, and a doubled maximum chain current. The latter will simplify running the accelerator with heavy ions at maximum terminal voltage. The pickup rings have been found to be useful in diagnosing malfunctions in the charge transport system.