Dissertation in Draft: Chapter XII

Date:: 1953

Reference:: PP/CRI/F/1/12

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

6/12

$presented here in detail,as while provisional sets of intensities for four of these have been obtained, the results, for various reasons, are not at the moment very accurate. Instead just one of two features wilT he mentioned. The variation of \F\ for 110 is shown in Figure . This method of presentation has been adopted because, since there is no centre of symmentry, one cannot be certain that the vector due to the salt will he parallel to that due to the salt-free protein. If it is not, then ¡F| will not go to zero, hut will merely pass through a minimum. It can easily be shown that the shape of the curve, when plotted with the co-ordinates of Figure , should he a hyperbola concave symmetrically upwards. In the limiting case where the two vectors are parallel and ]Pi goes to zero, the hyperbola degenerates into two straight lines. It can be seen that the experimental results suggest that 110 does not go through zero, but has a minimum value of about 300 electron. This is what one might expect if the lumpiness inside the molecules vfere not quite evenly distributed within its volume (defined as the region into which the salt does not enter). The electron density of the salt solution at which this minimum is reached is between 0.39 and 0.1+0 electons/iP. The corresponding value for the zero of the 001 reflexion is about 0.J+07 (Bragg,Perutz 1952 a). These two results suggest that there is no evidence that the bound water of haemoglobin is mainly on the outside of the ellipsoid. It can easily be shown that if the haemoglobin molecule could be regarded as an ellipsoid of a uniform density of 0.43 electron/Â^, surrounded by a layer of water, these two reflexions would not approach zero till the salt-concentration reached 0.43 or$

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Dissertation in Draft: Chapter XII

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