"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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    7 ^ • the crystal 4 1 Is often possible for small molecules to diffuse into the crystal without disturbing the arrangement of the protein molecules to any approiable extent« The salt concentration of the crystal nay he changed in this way, or, if the crystal is srrown from alcohol-water mixtures, the concentration of the alcohol may he alwtered, or a different alcohol allowed to penetrate the crstal. Even comparitively lar,see molecules, like dyes, «an sometimes diffuse into protein crystals, and it would not he surprising if an enzyme inhibitor could he made to combine with the enzyme while the latter was in the form of a crystal. Naturally it may happen that such a combination will changa the unit cell somewhat, but it is quite possible tha+ the unit cell dimensions will hardly alter at all. Optical examination The optical examination m a s t, be done on the wet crystals immersed in its mother liquor, as the optical quality of the dry crystals is usually very poor. This restriction makes some of the usual optical measurements very akw&rd, and in practice '-he only properties measured are those which can be studied with reasonable convenience. It is often difficult , for example to view a rod-like crystal end on. The infra red and ultra, violet dichroism of protein crystals have been measure 1 in a few cases but, these techniques are outside the scope of this chapter. If the protein is conjugated with a molecule which absorbs in the visible region the crystal should be examined for dichroism2-?-*' I^ounti^vr Crystals To obtain X-ray pictures of a wet. protein crystal it is