Crystallization and initial X-ray diffraction studies of higher plant photosystem I

Complete photosystem I from a higher plant (pea; Pisum sativum) was isolated, purified and crystallized. The crystals diffract to 4 Å resolution using synchrotron radiation and belong to the monoclinic crystal system, space group P2₁, with unit-cell parameters a = 181.90, b = 190.24, c = 219.66 Å, β = 90.484°. Data sets from three crystals have been collected and were merged into a 4.4 Å resolution data set, taking advantage of the high isomorphicity observed for these crystals. Analysis of the self-rotation Patterson function suggests the possible presence of two PSI complexes in the asymmetric unit.