Structure of Insulin as indicated by Atomic Models

Abstract

THE molecule of insulin consists of polypeptide chains of two kinds linked together by cystine residues. The complete amino sequence in these chains is now known, thanks to the work of Sanger and his co-workers¹. The A chains of Sanger's acid fraction contain twenty-one residues and the B chain thirty residues. There are four half-cystine residues in the A chains and two in each of the B chains, and their positions in the residue sequence are A6, A7, All, A20 and B7, B19. The minimum molecular weight has generally been reported to be about 12,000; but recently a value of the order of 6,000 has also been put forward. If the former value is correct, there will be two A and two B chains in the molecule, while there can only be one of each if the latter value is confirmed. It follows that if the linking arrangement could be determined, the complete chemical structure of this protein molecule would be known. There are many conceivable ways of linking the chains together and in the case of four chains there are some hundreds. It would be a considerable advance towards determining the complete structure if all those which are sterically impossible could be eliminated.