The Effect of Thiol Reagents on the Chromogenicity of Proteins Towards the Folin - Ciocalteu Reagent

Abstract

A. Introduction As the field of biochemistry and its allied branches of physiology, immunology etc., developed it became increasingly necessary to have a reliable method of protein determination. The Folin method, as described, was one such method which gained a considerable following for many years. Some of the limitations and advantages are listed in the discussion. The quantitative isolation of aminoacids was first used in the determination of proteins. Up to 1912 this isolation of any one amino acid from the heterogeneous mixtures obtained after protein hydrolysis was extremely unreliable and beset with many practical difficulties, so that any chemical reaction using a particular reagent for any single amino acid was extremely valuable and worthy of further investigation. About this time, tyrosine, one of the least soluble of the amino acids, became the target for investigation in a number of research centres. A survey of the literature of this period,(1) however, shows that the determination of this amino acid, by way of its isolation in pure conditions, was at the best a tedious and difficult task. Partly because of these literature discrepancies, and partly "because they hoped to determine whether proteins contain other phenol derivations, Folin and Denis(1) decided it seemed worth-while to make tyrosine determinations with a new reagent on a few selected proteins. This new phenol reagent (2,3)was a solution containing 10% sodium tungstate, 2% phosphomolybdic acid and 10% phosphoric acid such that two ccs of the reagent gave a maximum color with 1 mg of tyrosine or uric acid.