Pauling s Left-Handed a-Helix

proposed there was the a-helix. Its formulation was the first and is still one of the greatest triumphs of speculative model building in molecular biology; it is the forerunner of the vast investment in computer-assisted molecular modeling in present-day research in structural chemistry. Nowadays, almost everyone is aware that the a-helix is right-handed (that is to say, if the thumb of the right hand points along the helix axis, then the helix turns in the direction indicated by the fingers of the right hand). Imagine my surprise when, a few months ago, I noticed that in the illustration of the Proceedings paper (Figure 2) the helix is drawn left-handed! This is not an error. The choice of a left-handed sense of helicity was made arbitrarily. As written in the paper: