Application to the solution of the heavy atom structure.

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Application to the solution of the heavy atom structure.

Three notable references to the use of MULTAN for the solution of the partial structure are by Navia et al [87] and Wilson [118] where the isomorphous differences between native and derivative structures were utilised, and Mukherjee et al [86] where Bijvoet differences were used. In the latter reference, heavy atom positions were determined for three structures: Cytochrome- containing two iron atoms per asymmetric unit, Pea Lectin with two manganese atoms in the asymmetric unit and a mercury derivative of -amylase with one mercury atom per asymmetric unit. In these cases Bijvoet differences were used for the calculation of normalised structure factors.

In each of the cases studied, the phase set with the highest combined figure of merit corresponded to the correct solution when compared with MIR results. For two of the structures however the heavy atom positions were displaced by 2.5 Å and 5.0 Å away from the refined MIR positions.

Mukherjee et al showed that the largest Bijvoet differences measured provide a reasonable estimate of the magnitude of the imaginary part of the heavy atom structure factor, since (from Eq. gif)

and for the largest 's where and are orthogonal we see that

This is convenient since MULTAN uses a set of largest normalised structure factors, 's, in the calculation of triple product relations. Thus the measured may be used directly as input to MULTAN in a manner similar to using for a small molecule.

Gwyndaf Evans
Fri Oct 7 15:42:16 MET 1994