IT is now some time since we first took X-ray powder photographs of crystalline pepsin kindly sent by Prof. J. H. Northrop, but no really satisfactory interpretation of these photographs presented itself because they show features which we have learnt recently to associate with the fibrous proteins1: even single crystals, so far as we could judge with the minute crystals available, appeared to give results similar to those produced by many crystals in random orientation. The two chief rings have spacings of about 11.5 A. and 4.6 A. at ordinary humidity, corresponding to the ‘side-chain’ spacing and the backbone spacing, respectively, of an extended polypeptide1.
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ASTBURY, W., LOMAX, R. X-Ray Photographs of Crystalline Pepsin. Nature 133, 795 (1934). https://doi.org/10.1038/133795a0
Die Naturwissenschaften (1937)