"X-ray analysis and protein structure"

Date:
1956
Reference:
PP/CRI/H/2/1
Catalogue details

Licence: In copyright

Credit: "X-ray analysis and protein structure". Source: Wellcome Collection.

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    sign, however; that is to say we have, to correspond with protein + heavy atom (protein plus heavy atom) either (+10) + (-2) (+8) or (-10) (+2) (-8) Which of these is correct we cannot yet tell. %at we do know, however, is that the amplitude due to the heavy atom is +2 ; and thus if we could have a unit cell with all the protein subtracted out, empty except for the heavy atom alone, the intensity of ±k±s the reflexion we are considering in its diffraction pattern 2 would be (+2) = 4« ! ^ e carl thus calculate, without making assumptions, the intensities in the diffraction pattern due to the heavy atom alone - the so-called difference intensities« To find the position of the heavy atom we carry out a 2 Patterson synthesis, known as a Difference Patterson synthesis or (¡&F) synthesis This shows us the vectors between the heavy atoms in each of the asymmetric units all the vectors involving atoms other than the heavy atom have been cancelled out of the cell/ and from this it is simple to obtain the position of the heavy atom relative to the symmetry elements of the cell* An example of this is given on Having found the heavy atom we can calculate its contribution to any particular reflexion. Let± us suppose that it comes out to + 1.7 for the reflexion % we have been considering. Allowing for experimental error this agrees with the