Dissertation in Draft: Chapter XII

Date:
1953
Reference:
PP/CRI/F/1/12
Catalogue details

Licence: In copyright

Credit: Dissertation in Draft: Chapter XII. Source: Wellcome Collection.

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    centre, and the lower curve for crystals without such a centre. It is obvious that there is no tendency towards a centro-symmetric intensity distribution. This is disappointing, though^- as=we^s3ìaì'! ■ sëe# it was not unexpected. It should he noted that the intensity of uT , which has a spacing of 41 $,is very small. It thus probably «as near the first an. zero of the transform of isolated haemoglobin molecule. This is in general agreement with the ellipsoidal models proposed by Bragg and Perutz (1952 a and b). The basal section of the three-dimensional Patterson presented a curious feature. As can be seen (Pig. ) it has the crude appearance of an ellipsoid with its major axis some 20° away from the a. axis, and in the negative quadrant. Bragg and Perutz (1952 a and b) have argued convincingly that the haemoglobin molecule can be roughly approximated by an ellipse with its major axis, either along 0- , or some 20° from a in the positive quadrant. The Patterson of an isolated elliptical molecule will have ellipsoidal € contours, with their major axis coinciding with that of the ellipsoid itself. However, in an actual unit cell, there will be overlapping effects and the result will not be so certain. It was therefore decided to calculât# the Patterson of a solid ellipsoid of uniform electron density, 5U»h x 5k»k x 70 £ , major axis perpendicular to c, placed in the monoclinic haemoglobin cell. The calculation was done by imagining the cell to shrink so that the ellipsoids became spheres and then evaluating the structure factors by th§, obvious method, using the transform of a solid sphere. Prom these intensities the basal section ( y = o) of the three-dimensional Patterson was calculated, and is shown in Pig. . It can be seen that the contours do -3-