Crystallization of hen egg-white avidin in a tetragonal form

Hen egg-white avidin has been crystallized at pH 5.7 from ammonium sulfate solutions. The crystals belong to the tetragonal space group P4(2)2(1)2, with unit cell edges a = b = 79.6 A, c = 84.3 A. Assuming a molecular weight of 15,600 per avidin monomer, this crystal form is compatible with the presence of a dimer in the asymmetric unit, and is suitable for a crystallographic structural investigation at high resolution.