The Molecular Weights of Proteins.

ONE of the most satisfactory features of recent advances in the X-ray analysis of compounds of high molecular weight has been the degree of co-ordination between the efforts of the structure analyst and those of the chemist. Especially is this true in the case of investigations of the structure of cellulose and its derivatives. The question of protein structure, however, appears to bring in its train problems of quite another order of complexity, and it does not seem to be at all clear what is connoted by the phrase `molecular weights of proteins'. Such X-ray photographs of fibrous proteins as have been obtained point to the periodic repetition of comparatively simple units with imperfect or variable side-linkages. In the quest for chemical data to correlate with these results, the crystallographer is at once brought up against the remarkable observations of Svedberg, that there are groups of soluble proteins of `molecular weights' which are simple multiples of 34,500. The present situation is most simply described by quotations from two recent letters ^{1, 2} to NATURE :-