"X-ray diffraction of protein crystals"

Date:
1954-1956
Reference:
PP/CRI/H/1/33
Catalogue details

Licence: In copyright

Credit: "X-ray diffraction of protein crystals". Source: Wellcome Collection.

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    site is occupied in only half the molecules the heavy a+om appears to the X-rays to be of only half the atomic number and therefore too lieht. It is not necessarily an advantage to attach more than one heavy ato® per asymétrie unit, as the extra ones may only confmse the situation. A number of lighter atoms (ray Bromine ) will not. be acceptable instáéd 0P a heavy atom except possibly in the case where they are bound together in a group of a defincite shape. Finally the unit cells of the protein with and without the heavy a+om should have identical cell dimensions. It can be seen that the chemical requirement of attaching one heavy atom, or at the roost two or + hree, with high efficiency onto a few specific sites is a formidable one. Any protein to which it can be rSone becomes a very favourable object for X-ray studies. It may be possible, for example, to find the t general shape of such a protein molecule rather quickly. It should not be forgotten that the active site of an enzyme offers srreat possibilities as a unique site of attachment, and that an e nay ra e inhibitor containing a heavy atom might rather easily fulfil the above requirements If such a case comes to the knowledge of an énzymologist he should certainly bring it to the attention of a protein crystallosrrapher. Program of work /-Y - , - yj' ; ; 1 In this section is se + out a typical program of a preliminary I .• i ► I examination as it m i Fht be ssa-e by a protein crystalographer. It / ' ' ¡ • • i * Syi i * is not suggested that the whole of + his program sho ild always be I \i / i: J i carried out, but it may serve as a guide to general practice.