Two-dimensional crystallization of catalase on a monolayer film of poly(1-benzyl-l-histidine) spread at the air/water interface

Two-dimensional (2D) crystals of beef liver catalase were prepared by adsorption to a film of synthetic polypeptide, poly(1-benzyl-l-histidine) (PBLH), spread at the air/water interface. The crystallization experiments were carried out in the pH range of 4.8-6.4 for catalase solutions at low concentration (10 μg/ml). The pH-dependence suggested an electrostatic interaction in the binding of catalase to the PBLH film. At lower pH, small crystals were formed at a low binding rate, and at higher pH the binding was rapid and densely-packed 2D arrays with poor crystallinity were formed. To stimulate crystal growth, a thermal treatment was applied. One-shot heating of the interfacial catalase-PBLH film to 35-40°C was remarkably effective to form larger 2D crystals. The structure of catalase 2D crystals has been analyzed by Fourier filtering of the transmission electron micrographs. The crystal form is a new one, containing four catalase molecules in the unit cell with lattice parameters of a = 187 ○A, b = 225 ○A and γ = 92.8°.