Nature of the Linkages in Proteins

THERE is now a considerable amount of agreement that the polypeptides in the protein molecule are held together by cross-linkages1, but so far crucial experiments, from which the exact nature of these linkages may be deduced, are lacking. The only logical procedure is therefore to consider in turn all possible types of link and to investigate experimentally the deductions to be made from those which pass the qualifying test of being geometrically feasible. Among the links so far proposed are: (a) hydrogen bonds2,3,4, (b) cyclol links4,5,6 and (c), as a deduction from (b), hydroxyl bonds4,5.