On the optical rotatory power of crystalline ovalbumin and serum albumin

Abstract

The need for a physical method by means of which it would be possible to recognise a chemical individual of the protein group of compounds has undoubtedly been one of the factors contributing to the difficulty of research into the chemistry of the proteins. The present methods of chemical analysis do not nearly approach sufficient accuracy to distinguish between successive recrystallisations of a protein substance. The first serious effort to prove that an individual protein could be isolated is to be found in the publication of Hopkins (1900). It was here shown that a protein could be prepared with a constant specific rotation for successive recrystallisations and for material obtained from different sources. Unfortunately, this desirable physical constant, which is independent of the degree of colloidal dispersion, has been shown to vary with variations in physical and chemical conditions. Thus Alexander (1896) found the specific rotation of certain globulins varied according to the concentration of the protein and of salt present. An investigation of this phenomenon by Pauli, Samec and Strausz (1914) confirmed the observations of Hopkins (1900) and of Osborne (1899) that the presence of neutral salts has no influence on the optical rotation of a protein. The addition of acids and of alkalies they found to increase the rotation of polarised light, while the degree of change depended upon the nature of the anion in the case of an acid and of the kation in the case of a base. These observations were made, unfortunately, with the mixture of proteins contained in ox or horse serum which had simply been dialysed until salt-free. The nature of these changes may find explanation in a tautomeric rquilibrium of the lactam-lactim type in the protein main chain when in aqueous solution, as suggested by Robertson (1912) and Sörensen (1912), and to which view Pauli inclines. R—CO—NH—R ⇌ R—C(OH) = N—R. Lactam formula Lactim formula.