Crystallization and preliminary X-ray analysis of the ternary complex of procarboxypeptidase A from bovine pancreas.

The ternary complex of procarboxypeptidase A, chymotrypsinogen C and proproteinase E from bovine pancreas has been crystallized using the sitting drop vapour diffusion method. The success in obtaining crystals has been found to be critically dependent on the prevention of autolysis of the complex. In preliminary stages, crystals twinned by merohedry were obtained from a solution containing MgCl2 and polyethylenglycol 400 as precipitating agent. Later on, untwinned ones could be grown employing CaCl2 instead of MgCl2. These latter crystals belong to the rhombohedral system and to the spacegroup R3 with cell dimensions a = b = 188.5 A and c = 82.5 A. Consideration of the possible values of Vm accounts for the presence of one ternary complex molecule-oligomere per asymmetric unit. The crystals diffract beyond 2.6 A resolution and are suitable for X-ray analysis.