Crystallographic dyads

Contact surface areas for the monomer-monomer interactions within the homotetramer present in both crystal forms were calculated using the algorithm of Lee and Richards (94). It is evident from these calculations (74) that the contact surface areas between the two dimers about the crystallographic dyad are by far the largest. Ascorbate oxidase... 

Assume, however, that the asymmetric unit is composed of two or more identical copies of a molecule. These may be related by exact rotational symmetry, such as a dyad or triad, that is not coincident with any crystallographic operator and, hence, is not a part of the space group symmetry. The molecules may also be related by some completely general rotation plus translation. The asymmetric unit will give rise, in either case, to a continuous transform that is essentially a superposition of the transforms of the two independent molecules. This is illustrated schematically in Figure 8.9. The two molecular transforms are identical because the two molecular structures are the same, but the two transforms will be rotated relative to... 

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