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Figure 1.
Figure 1 Schematic representation of the two tetramers in the
monoclinic crystals. S and L indicate the occupation of the
combining site by lactose and a loop from a neighbouring
molecule, respectively. Four combining sites are unoccupied. P
represents the molecular dyad. R1 and R2 represent the twofold
axes that relate A and D, and B and C, respectively. P, R1 and
R2 do not intersect, but pass through a line represented by Q.
In the orthorhombic crystals, which grow only in the presence of
sugar, the crystallographic asymmetric unit contains one
tetramer in which all the subunits are sugar-bound.
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