CRYSTALLIZATION AND PRELIMINARY CRYSTALLOGRAPHIC DATA FOR ACETOHYDROXY ACID ISOMEROREDUCTASE FROM SPINACIA-OLERACEA

Acetohydroxy acid isomeroreductase (EC 1.1.1.86) is one of the enzymes involved in branched-chain amino acid biosynthesis. The enzyme from s pinach (Spinacia oleracea) leaves has been crystallized using the hang ing drop vapour diffusion method. The free enzyme crystallized from po lyethylene glycol solutions, but these crystals were unsuitable for X- ray diffraction analysis. In the presence of NADPH, Mg2+ and a reactio n intermediate analogue (2-dimethylphosphinoyl-2-hydroxy acetic acid ( Hoe 704) or N-hydroxy-N-isopropyloxamate (IpOHA)), much better crystal s were obtained. Crystals grown from ammonium sulphate belong to space group P2(1) with cell dimensions a = 193.78(7) Angstrom, b = 63.69(2) Angstrom, c = 112.84(1) Angstrom and beta = 121.22(1)degrees. The mol ecular mass of the protein, the volume of the unit cell, and crystal d ensity measurements indicated that the asymmetric unit contains two di mers. X-ray diffraction patterns showed measurable reflections to beyo nd 2.5 Angstrom.