PRELIMINARY X-RAY STRUCTURE ANALYSIS OF ACC DEAMINASE Atsushi Horiuchi, Min Yao, Atsushi Nakagawa, Isao Tanaka and Mamoru Honma*, Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo 060, Japan, *Department of Bioscience and Chemistry, Faculty of Agriculture, Hokkaido University, Sapporo 060, Japan

1-Aminocyclopropane-1-carboxylic acid(ACC) is isolated from several plant tissues including pears and apples, and regarded as a key intermediate in the biosynthesis of ethylene, a plant hormone that affects diverse growing and developmental processes, including fruit ripening, leaf and flower senescence, and stress responses. ACC is the simplest compound in which amino and carboxyl groups bind to cyclopropane ring directly. The enzyme ACC deaminase catalizes opening of this ring to give a-ketobutyrate.

ACC deaminase from a yeast Hansenula saturnus has been crystallized by a hanging-drop vapour diffusion method. The diffraction data from native crystal has been collected to 4.0 Å resolution with Rmerge=11.3% (82.1% of expected reflections) on a Weissenberg camera using synchrotron radiation at Photon Factory (KEK,Japan).The crystals belong to C222₁ space group with cell dimensions of a=276.7, b=66.1 and c=187.1 Å. Assuming two dimers of an estimated molecular weight of 69,000 per asymmetric unit, Vm was calculated to be 3.0ų/Da and solvent volume fraction was 58 %. Assuming three dimers per asymmetric unit, Vm was calculated to be 2.0ų/Da and solvent volume fraction was 38%. Diffraction data set of PHMBS derivatives was collected to 4.0Å resolution with Rmerge=12.8% (89.0% of expected reflections). From difference Patterson and anomalous difference Patterson maps of PHMBS derivative, we could find heavy atom peaks. Phasing and a searching for further heavy-atom derivatives for multiple isomorphous replacement method are now in progress.