Letter | Published:

Constitution of the Keratin Molecule

Nature volume 130, page 401 (10 September 1932) | Download Citation



IN dealing with my 1 comments upon their communication 2 under this title, Speakman and Hirst 3 describe as erroneous my statement that “the guanidine group of arginine does not … yield nitrogen with nitrous acid under the usual conditions”. By “usual conditions” I naturally imply those generally adopted in determinations of amino-nitrogen in the course of protein analysis as described by van Slyke,4 5 that is to say, contact between acid nitrate solution and amino-body at room temperature, for 3–5 minutes in the case of mono-amino acids and for ½–1 hour in the case of the hexone bases or proteins. Under these conditions the guanidine group of arginine is practically unaffected. The work of Plimmer 6 to which Speakman and Hirst refer is, of course, well known to me, and in that paper it is stated that any error introduced by reaction of the guanidine group of arginine in a 1-hour determination is inappreciable. With longer reaction times, correspondingly greater decomposition does occur.

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  1. Onderstepoort Veterinary Research Laboratory, Pretoria, South Africa, July 13.



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