Proinsulin: Crystallization and preliminary x-ray diffraction studies

Bovine proinsulin has been crystallized under a variety of conditions at both neutral and acid pH. Microtechniques were employed with sample weights of about 200 mug and volumes of 5-20 mul. The crystalline preparations all differ from each other morphologically.X-ray photographs of one form, tetragonal bipyramids grown at pH 3 with added ammonium sulphate solution, established the space group P4(1)2(1)2 (or its enantiomorph P4(3)2(1)2). The cell dimensions are a = 50.8 +/- 0.2 A, c = 148.0 +/- 0.4 A. The asymmetric unit in this form is a dimer of proinsulin which is also the dominant species in solution at this pH.